Banana Cake with Coffee Walnut Buttercream

It was a familiar situation: it was Thursday evening and I had committed to bringing a cake to school. Instead of going home and baking, we went out to dinner. So then it was 10 pm on a Thursday, I still had a cake to bake and frost, and I had to get up at 6 the next day.

So I decided to try a new recipe from Vintage Cakes to use up some of my frozen ripe bananas and make the cake seem “healthy.” The batter was easy to make and in no time my cakes were in the oven. Then I turned the page to the buttercream recipe. It wanted me to grind the walnuts into a paste, then it called for corn syrup and bourbon. Looked like a good recipe, but not a good one to attempt at 11 pm on a school night. So instead I turned to a stand-by buttercream from Baked and added a couple of additions. Below, I’ve included both buttercream options.

The cake itself was a hit. I think we baked it too long (the skewer did not come out clean, but of course it could have skewered a banana bit), so it was a bit hard to cut without a serrated knife. But the combination of flavors and textures was delicious. It was gone in a flash!

Banana Cake with Coffee Walnut Buttercream

From Vintage Cakes (alternative buttercream recipe from Baked Elements)


2 1/2 cups (12 1/2 ounces) all purpose flour

1 1/2 teaspoons baking powder

1/2 teaspoon fine sea salt

1/4 teaspoon baking soda

1 1/2 cups mashed ripe bananas (about 3)

3/4 cup buttermilk, at room temperature

1 cup (8 ounces) unsalted butter, at room temperature

2 cups (14 ounces) sugar

1 tablespoon pure vanilla extract

4 eggs, at room temperature

Buttercream (see below for two options)


Center an oven rack and preheat the oven to 350F.

In a large bowl, sift together the flour, baking powder, salt, and baking soda, then whisk the ingredients with a hand whisk.

In a small bowl, combine the banana with the buttermilk.

In the bowl of a stand mixer fitted with the paddle attachment, cream the butter, sugar, and vanilla together on high speed until fluffy, about 5 minutes. Stop the mixer frequently and scrape the paddle and the sides of the bowl with a rubber spatula. Blend in the eggs one at a time. With the mixer on low, add the flour mixture in three parts, alternating with the banana mixture in two parts, beginning and ending with the flour. After each addition, scrape the bowl. Stop the mixer before the last of the flour has been incorporated and complete the blending by hand with a rubber spatula.

Divide the thick batter evenly among three 8-by-2-inch round cake pans (greased and bottoms lined with parchment paper circles). Tap the pans on the counter to settle. Bake until the centers spring back when lightly touched, 28 to 30 minutes. Cool the cakes in their pans on a wire rack for 30 minutes. Flip them out and let them continue to cool on the rack, top side up, until they reach room temperature. Leave the parchment paper on until you assemble the cake.

To assemble the cake, lay one of the cakes top side up on a cake plate. Using a metal spatula, frost the top with buttercream out to the edge of the cake. Stack the second cake top side up on top of the frosted cake and spread more buttercream on top of it. Stack the last layer of cake top side up on top. Look for any frosting that may have oozed out of the sides and spread it along the sides of the cake. Apply a thin layer of frosting all over the cake to create a “crumb coat.” Place the cake in the refrigerator until the frosting is firm, about 10 minutes. Take it out and frost the cake with the remaining buttercream, using your spatula to make decorative swirls.

Buttercream  adapted from Baked Elements

(Baked Elements actually has a recipe for Coffee Buttercream which I did not use in this case, partly because I don’t have any coffee extract on hand. Instead, I very slightly adapted the honey buttercream recipe for the Aunt Sassy Cake.)


1 1/2 cups sugar

1/3 cup all-purpose flour

1 1/2 cups whole milk

1/3 cup heavy cream (full disclosure: I used 200 ml of heavy cream and the remainder skim milk)

1 1/2 cups (3 sticks) unsalted butter, soft but cool, cut into small pieces

1 teaspoon pure vanilla extract

1 teaspoon Nescafe instant espresso powder

1 cup chopped walnuts


In a medium, heavy-bottomed saucepan, whisk the sugar and flour together. Add the milk and cream and cook over medium heat, whisking occasionally, until the mixture comes to a boil and has thickened, about 10 to 15 minutes.

Transfer the mixture to the bowl of a standing mixer fitted with the paddle attachment. Beat on high speed until cool (this takes at least 7 to 9 minutes of mixing; you can speed up the process by pressing bags of frozen berries or frozen corn against the sides and bottom of the mixing bowl). Reduce the speed to low and add the butter; mix until thoroughly incorporated. Increase the speed to medium-high and beat until the frosting is light and fluffy, 1 to 2 minutes.

Add the vanilla and coffee powder and continue mixing until combined. If the frosting is too soft, put the bowl in the refrigerator to chill slightly, then beat again until it is the proper consistency. If the frosting is too firm, set the bowl over a pot of simmering water and beat with a wooden spoon until it is the proper consistency.

To assemble the cake:

Spread about 1 1/4 cups of frosting on top of the first cake layer. Sprinkle about 1/4 cup of your chopped walnuts on top of the frosting. Add a layer of cake, another 1 1/4 cups of frosting, another 1/4 cup of chopped walnuts. Spread a thin layer of frosting to make the crumb coat, refrigerate for 10 to 15 minutes to firm the frosting, then frost with the remaining buttercream until beautiful. Sprinkle the remaining 1/2 cup chopped walnuts decoratively on the top.


Coffee Walnut Buttercream from Vintage Cakes


1 cup (4 ounces) walnuts, toasted

1/4 cup corn syrup

1/4 cup bourbon

2 tablespoons instant espresso powder

5 egg whites

1 1/4 cups (8 3/4 ounces) sugar

1/4 teaspoon cream of tartar

1 1/2 cups (12 ounces) room temperature unsalted butter, cut into 1-inch pieces

1/4 teaspoon fine sea salt



First, make a walnut-espresso paste: Puree the walnuts in a food processor until they just begin to form a paste. Add corn syrup, bourbon and espresso powder and blend until combined. Set aside.

Then, make the buttercream: Using a hand whisk, whisk together the egg whites, sugar, and cream of tartar in the clean bowl of a stand mixer. Place the bowl over (not in) a saucepan of simmering water. The egg white mixture will be gloppy and thick, but as the mixture begins to warm up, it will become more fluid. Continue to gently whisk the mixture until it is very hot to the touch (130F on a candy thermometer).

Move the bowl to the stand mixer and, using the whisk attachment, whip the whites on medium-high speed until they have tripled in volume and are thick and glossy and hold stiff peaks (like meringue), 3 to 4 minutes. Turn the mixer down to medium-low speed until the mixing bowl is just cool to the touch, 1 to 2 minutes. Kick the mixer back up to medium-high speed and add the butter one piece at a time, adding the next piece just as the previous one has been incorporated. Stop the mixer every so often to scrape down the escaping buttercream from the sides of the bowl. At some point, the buttercream will take on a curdled appearance; don’t worry, this is normal. Just keep on mixing until it comes together. Once all the butter is incorporated and the frosting is fluffy and creamy, blend in the vanilla and walnut-espresso paste.

Covered with plastic wrap, the buttercream will last 2 days at room temperature or 7 days in the refrigerator. If refrigerated, the buttercream must be brought to room temperature before you use it. Either way, the buttercream must be rewhipped – either by hand if kept at room temperature or with a mixer if refrigerated – before you frost a cake with it.

To assemble the cake, use 3/4 cup of buttercream between layers.

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