Steamed Vietnamese honeycomb cake, known as banh bo nuong or banh bo hap, is a uniquely textured Southeast Asian treat that gets its name from the honeycomb-like pattern of holes that form throughout the cake as it steams. This spongy, bouncy cake has a wonderfully light and airy texture that’s almost chewy, with a subtle coconut flavor and delicate sweetness that’s not overwhelming. The magic happens during steaming when the combination of tapioca starch and leavening agents creates those signature bubbles and tunnels throughout the cake, making it look almost like actual honeycomb. The result is a dessert that’s fun to look at, delightful to eat, and completely different from Western-style baked cakes. Whether you’re exploring Vietnamese desserts for the first time, want to impress guests with something unique, or just love interesting textures and flavors, this honeycomb cake is a wonderful adventure. It’s traditionally tinted green with pandan but can be made in various colors and flavors.
Serving Quantity: Serves 8 to 10 people
Cooking Time: 1 hour and 15 minutes (including 15 minutes prep time, 45 minutes steaming time, and 15 minutes cooling time)
1. Ingredients
- One cup tapioca starch (not tapioca flour)
- Three-quarters cup all-purpose flour
- One cup granulated sugar
- One can coconut milk, full-fat (13.5 ounces)
- One cup water, room temperature
- Three large eggs, room temperature
- One tablespoon vegetable oil, plus more for greasing
- Two teaspoons instant yeast
- One teaspoon baking powder
- Half teaspoon salt
- One teaspoon vanilla extract
- Half teaspoon pandan extract (or green food coloring, optional)
- One tablespoon warm water (about 110 degrees) for activating yeast
2. Prepare Your Steaming Setup
Before you start mixing, set up your steaming apparatus because the batter needs to go into the steamer immediately after mixing. Fill a large pot or wok with water, about 2 to 3 inches deep, and bring it to a boil over high heat. Place a steaming rack inside that sits above the water level. If you have a traditional bamboo steamer, that works perfectly. Make sure your setup can accommodate your cake pan. You’ll need a 9-inch round cake pan or an 8-inch square pan that fits inside your steamer with some clearance for steam circulation.
3. Prepare the Cake Pan
Generously grease your cake pan with vegetable oil, making sure to coat the bottom and sides thoroughly. Vietnamese honeycomb cake can be quite sticky, so don’t skimp on the oil. You can also line the bottom with parchment paper and grease the paper for extra insurance. Set the prepared pan near your steaming setup so it’s ready to go as soon as you finish mixing the batter. Having everything ready prevents delays that could affect the cake’s texture.
4. Activate the Yeast
In a small bowl, combine the instant yeast with one tablespoon of warm water, around 110 degrees. The water should feel warm but not hot to the touch. Stir gently and let it sit for about 5 minutes until it becomes foamy and bubbly on top. This proves that your yeast is alive and active. If it doesn’t foam, your yeast might be dead or your water was the wrong temperature, and you’ll need to start over with fresh yeast. Active yeast is crucial for creating those signature honeycomb holes.
5. Mix the Dry Ingredients
In a large mixing bowl, whisk together the tapioca starch, all-purpose flour, baking powder, and salt. Make sure there are no lumps in the tapioca starch, as they won’t dissolve during mixing. Whisk thoroughly for about 1 minute to aerate the dry ingredients and ensure everything is evenly distributed. The combination of tapioca starch and regular flour creates the unique bouncy, chewy texture that makes this cake special. Set this bowl aside.
6. Combine Wet Ingredients
In another large bowl or the bowl of a stand mixer, whisk together the eggs and sugar vigorously for about 2 minutes until the mixture becomes pale and slightly frothy. Don’t skip this step as beating air into the eggs helps create structure. Add the coconut milk, room temperature water, vegetable oil, vanilla extract, and pandan extract or food coloring if using. Whisk everything together until completely smooth and uniform. The mixture should be quite liquid at this stage.
7. Add the Activated Yeast
Pour the activated yeast mixture into the bowl with the wet ingredients. Whisk it in thoroughly so the yeast is evenly distributed throughout the liquid. The yeast will start working immediately to create bubbles, which is exactly what you want. These bubbles, combined with the steam and the properties of tapioca starch, create the honeycomb effect. Work relatively quickly from this point forward because the yeast is already activated.
8. Combine Wet and Dry
Pour the wet ingredients into the bowl with the dry ingredients. Use a whisk to mix everything together, stirring gently but thoroughly until you have a smooth batter with no lumps. Don’t overmix or beat vigorously, just stir until everything is combined. The batter will be quite thin and liquid, similar to pancake batter or even thinner. This is exactly right. The tapioca starch needs this liquid consistency to create the proper texture during steaming.
9. Let the Batter Rest Briefly
Let the mixed batter sit for about 5 minutes at room temperature. During this time, you’ll start to see small bubbles forming on the surface as the yeast begins to work. These bubbles are a good sign. Don’t let it sit too long though, as you want most of the bubble action to happen during steaming. While the batter is resting, make sure your steaming water is at a rolling boil and ready to go.
10. Pour into Pan and Steam
Give the batter one final gentle stir to redistribute any ingredients that may have settled. Pour the batter into your prepared greased pan. The pan should be about three-quarters full to allow room for the cake to rise during steaming. Carefully place the filled pan into your preheated steamer, positioning it on the rack above the boiling water. Cover the steamer with a lid. If using a metal lid, wrap it in a kitchen towel to prevent condensation from dripping onto the cake, which can create wet spots and affect the texture.
11. Steam Without Peeking
Steam the cake over high heat for 40 to 45 minutes without opening the lid. This is crucial. Opening the lid releases steam and heat, which will cause the cake to collapse and prevent proper honeycomb formation. The cake needs consistent, high heat and steam throughout the entire cooking time. You should hear the water boiling steadily and see steam escaping from the edges of the lid. If your heat is too low and the water isn’t boiling vigorously, the cake won’t develop its signature texture.
12. Check for Doneness
After 40 minutes, you can carefully lift the lid to check if the cake is done. Insert a bamboo skewer or toothpick into the center of the cake. It should come out clean with no wet batter clinging to it. The top of the cake should look set and feel slightly springy when touched gently. The color should be uniform throughout. If the skewer comes out with wet batter, cover and steam for another 5 minutes, then check again. Don’t undercook or the texture will be gummy instead of bouncy.
13. Cool in the Pan
Once the cake is fully cooked, carefully remove the pan from the steamer using oven mitts or thick towels, as it will be extremely hot. Place the pan on a wire cooling rack. Let the cake cool in the pan for about 10 to 15 minutes. Don’t try to remove it from the pan while it’s hot or it will tear and fall apart. As it cools, the cake will firm up and pull away slightly from the sides of the pan, making it easier to remove.
14. Unmold and Observe the Honeycomb
After the cooling period, run a knife around the edges of the pan to loosen the cake. Place a plate or cutting board over the top of the pan and carefully flip everything over. The cake should release cleanly. Flip it right-side up so the smoother top is facing up. Now you can see the beautiful honeycomb pattern of holes throughout the cake. The holes should be varied in size, creating that signature bubble texture. The cake should have a slightly shiny surface and a gorgeous green color if you used pandan.
15. Slice and Serve
Let the cake cool completely to room temperature before slicing for the best texture, about 30 minutes. Use a sharp knife to cut the cake into squares, diamonds, or wedges. Wipe the knife clean between cuts for the neatest slices. The cake should be bouncy and slightly chewy with a light, airy structure full of holes. Serve at room temperature or slightly chilled. Vietnamese honeycomb cake is traditionally enjoyed as a snack or light dessert, perfect with tea or coffee.
16. Texture and Appearance
A perfectly made honeycomb cake should have numerous holes of varying sizes throughout, creating a sponge-like appearance. The texture should be bouncy and slightly chewy, almost like a very soft, airy mochi. It should not be dense, gummy, or heavy. The top should be smooth while the interior is riddled with tunnels and bubbles. The cake should spring back when pressed gently. If your cake is too dense, you may have undermixed the batter or not steamed at a high enough temperature.
17. Storage Instructions
Store leftover honeycomb cake in an airtight container at room temperature for up to 2 days. The texture is actually best on the day it’s made, but it remains good for a couple days. You can also refrigerate it for up to 5 days, though chilling makes it slightly firmer. Bring it to room temperature before serving for the best texture, or warm individual pieces in the microwave for 10 to 15 seconds. Don’t freeze this cake as the texture changes dramatically and becomes unpleasant when thawed.
18. Nutrition Information Per Serving
- Calories: 245
- Total fat: 8 grams
- Saturated fat: 6 grams
- Cholesterol: 55 milligrams
- Sodium: 180 milligrams
- Total carbohydrates: 40 grams
- Dietary fiber: 1 gram
- Sugars: 21 grams
- Protein: 4 grams
19. Helpful Tips for Perfect Vietnamese Honeycomb Cake
- Use tapioca starch, not tapioca flour, as they’re different products that will give completely different results.
- Make sure your steaming water is at a rolling boil before adding the cake for proper heat and steam circulation.
- Don’t open the steamer lid during cooking as this releases heat and steam, causing the cake to collapse.
- Wrap metal lids in a towel to prevent water condensation from dripping onto the cake and creating wet spots.
- Use room temperature ingredients so the yeast activates properly and works efficiently throughout the batter.
- Work quickly once the yeast is activated as you want most of the rising action to happen during steaming.
- Grease the pan very generously as this cake can be quite sticky and difficult to remove otherwise.
- Let the cake cool in the pan before unmolding or it will tear and fall apart from being too delicate when hot.
- Try different extracts like coconut, vanilla, or even cocoa powder for chocolate versions with varied flavors.
- If your cake is too dense, increase the steaming temperature or ensure your yeast was fresh and properly activated.
