The Cake Slice January 2013: Banana Cake with Coffee Walnut Buttercream

I was intrigued when this cake was voted as this months bake. Banana and walnut cake is a classic and so is coffee and walnut, but banana, coffee and walnut was not something I had come across before.

The cake was a plain banana cake, with the coffee and walnut coming in via a smooth meringue based frosting to which you add a nutty coffee spiked puree. I love meringue based buttercreams like this as they are silky smooth and creamy without the usual grittiness you can sometimes get from the more traditional butter and icing sugar buttercreams.

The recipe made a triple layer cake which was far too much for me, so I halved the recipe and baked them as cupcakes instead. You can see from the photos that the walnuts on top of my cupcakes look suspiciously like pecans, which is because they are! Having just bought a bag of pecans I decided to use those instead of walnuts in the buttercream, the flavour combinations still worked together well.

Things got off to a bad start when my digital scales ran out of batteries half way through weighing gout the cake ingredients. It needed a big rectangle battery which I didn’t have. I improvised with a coffee mug and tried to work out American measurements which seemed to work ok. I then didn’t have a sugar thermometer for measuring the temperature of the meringue for the buttercream, and to top it all when I added my nutty coffee concoction to the fluffy mounds of frosting the buttercream split and went very runny. Argh!

I put the buttercream in the fridge for several hours and thankfully it seemed to come together but not quite as light and fluffy as it should do. It tasted divine though, so silky, it just melted in the mouth. I really liked the boozy coffee nutty flavour too (yes there is booze in the buttercream too!)

The cake part however I found slightly disappointing. The cakes were quite dense and closely textured and only had the faintest flavour of banana. I made sure to use ripe bananas too. The super soft and creamy frosting made up for the slightly bland cake though. The cakes were quite moist, but by the following day I found them to be a little dry.

I’m pleased I tried the recipe but I wouldn’t make them again. I love the idea of the boozy nutty coffee cream though, so will try and use these flavours together another time. Click here to see the other Cake Slice Bakers banana cakes

Banana Cake with Coffee Walnut Buttercream

(Recipe from Vintage Cakes by Julie Richardson)

Banana Cake
375g gluten free plain flour

1½ tsp baking powder

½ tsp salt

¼ tsp bicarbonate of soda

3 ripe mashed bananas (around 270g peeled weight)

170ml buttermilk

240g butter

420g caster sugar

1 tbsp vanilla extract

4 eggs

Coffee Walnut Buttercream
120g toasted walnuts (I used pecans)

50ml corn syrup (I used golden syrup)

50ml Bourbon (I used amaretto)

2 tbsp instant espresso powder

6 egg whites

260g caster sugar

¼ tsp cream of tartar

440g butter, cut into small cubes

2 tsp vanilla extract

Banana Cake
Preheat the oven to 180C. Grease and line 3 x 8inch round cake tins.

Mix together the flour, salt, baking powder and bicarbonate of soda and set on one side. In a small bowl mix together the mashed banana, vanilla and buttermilk and set to one side.

In a large bowl, cream together the butter and sugar until fluffy. Add the eggs, one at a time, beating well between each addition.

Add the flour mixture in three batches, alternating with half the banana buttermilk mixture in-between each flour addition.

Divide the batter evenly between the three cake tin and smooth out the surface.

Bake for 28-30 minutes until the cakes spring back when lightly pressed. Allow the cakes to cool in their tins for 30 minutes before turning out onto a wire rack to cool completely.

Coffee Walnut Buttercream
Start by making a nut paste. Puree the toasted walnuts in a food processor until they begin to form a paste. Add the corn syrup, bourbon and espresso and puree until combined. Transfer to a small bowl and set aside.

Now make the buttercream. Lightly whisk the egg whites, sugar and cream of tartar together in a large heatproof bowl. Place the bowl over a pan of gently simmering water and continue to whisk until the mixture becomes white, thick and sticky. It should read 55C/130F on a sugar thermometer.

Remove the bowl from the heat and whisk using an electric mixer, until the mixture has tripled in volume, become glossy and holds a stiff peak. Reduce the whisking speed and continue to beat until the mixture is cool to the touch.

Once cool, keep whisking while slowly dropping in small cubes of the butter. Keep beating until it is all combined.

Add the vanilla and your pre-prepared nut espresso mixture and beat thoroughly to combine.

It can now be used to decorate your cake or covered with clingfilm and left in the fridge for up to two days. If refrigerated, bring the mixture back to room temperature before lightly whisking and using.

Assembly
To assemble the cake, lay one of the cakes, top side up on a serving plate. Spread over around one-fifth of your buttercream and top with another cake layer. Spread this with another fifth of your buttercream and top with the final cake layer.

Use the rest of the frosting to cover the top and sides of your cake.

For a neater finish, allow only a thin crumb coat of buttercream to the outside of the cake before placing in the fridge of firm up for 30 minutes. Then cover the cake with a thicker layer of buttercream.

Store in the fridge. Makes 1 x triple layer 8inch cake.

Notes:
I halved the cake recipe above and ended up with 10 cupcakes. The cake mix doesn’t rise much, so you can fill the paper cases almost to the rim.

I then used only a third of the buttercream recipe to decorate my cupcakes. I also substituted pecans in place of the walnuts.

My buttercream split when I added the nut espresso mixture, but I placed it in the fridge for two hours and then gave it a quick mix before using. It wasn’t perfect, but it did hold together