Banana Cake with Fudgy Frosting

[UPDATE: If you are making this, I suggest adding 1/2 to 3/4 cup of the evaporated milk, then adding more if the frosting is too thin. I've made a few bad batches- all because I added too much liquid.]

I had a fantastic potluck last night. I contributed a mushroom tart and this banana layer cake. We also had miso soup, mac and cheese, vegetarian chili, tofu scramble with gorgonzola, sweet and spicy nuts, and three bottles of wine.

The last time I hosted a potluck I baked a recipe i'd never tried. It made me stressed, so this time I was determined to cook something familiar. I've made this cake seven or eight times and I knew it'd be fantastic. It has a frosting that I actually enjoy eating- it's rich, smooth, and has good texture even when it's cold. I have no problem piling it on.

The Weekend Baker is one of my favorite cookbooks. It gives weight conversions for all the ingredients and suggestions for preparing components in advance. I baked the cake layers two days early and left them on the counter in gallon-sized ziplock bags. I cut the bags away the night before and frosted the cake, then pulled it out of the fridge two hours before the potluck.

Everyone loved it. Liz said something like: "Lisa, how do you not make this cake all the time and get really fat?" I made an effort to post the recipe quickly because multiple people requested it.

The consitency of the frosting can vary depending on the chocolate and butter you use. I suggest under-measuring the milk, and if the frosting seems too thin try adding a little more butter. Sometimes my frosting is firm enough to pipe, but sometimes it isn't. I used unsweetened baking chocolate from Trader Joes and I really preferred it to normal Bakers squares.

Banana Layer Cake with Fudgy Frosting
adapted from Abigal Johnson Dodge's The Weekend Baker

For the cake:
2 2/3 cups (340g) all purpose flour
1 tbsp baking powder
1/2 tsp table salt
1/2 tsp baking soda
16 tbsp (2 sticks) unsalted butter, at room temperature
1 3/4 cups (397g) granulated sugar
3 medium, very ripe bananas (397g total including peel), peeled
2 tsp vanilla extract
4 large eggs
1/2 cup buttermilk
3/4 cup (85g) chopped walnuts, optional

For the fudgy frosting:
6 oz unsweetened chocolate, chopped
1 1/3 cups (298g) granulated sugar
1 cup evaporated milk (not sweetened condensed)
6 tbsp (85g) unsalted butter, cut in 2 pieces
1 tbsp pure vanilla extract
1/2 tsp table salt

toppings: chopped toasted walnuts, other nuts, or toasted shredded unsweetened dried coconut.

1. To make the cake: position an oven rack on the middle rung. Heat the oven to 350F (180C). Grease and flour the bottom and sides of two 9x2 inch (22.75x5cm) round cake pans, tapping out the excess flour. You can also line the bottoms of the pans with parchment to ensure easy and clean removal.

2. In a medium bowl, combine the flour, baking powder, salt, and baking soda. Whisk until well blended. In a large bowl, beat the butter with an electric mixer (or a stand mixer with the paddle attachment) on medium high speed until smooth. Add the sugar and beat until well combined. Add the bananas and vanilla and beat until well blended and only small bits of banana remain. Add the eggs two at a time, beating well after each addition. The mixture will look curdled and a bit lumpy. Don't worry, it will all come together. Add half of the flour mixture and mix on low speed just until blended. Add the buttermilk and mix just until blended. Add the remaining flour and mix until blended. Stir in the walnuts, if using. Scrape the batter into the prepared pans, dividing it evenly.

3. Bake until the tops are light brown and a toothpick or cake tester inserted into the center of one layer comes out clean, about 30 minutes. Transfer the pans to racks and let cool for about 15 minutes. Run a thin knife around the sides of each pan to loosen the cake. Invert the layers onto the racks, lift off the pans, and let cool completely.

4. To make the frosting: While the cake is baking, make the frosting. Melt the unsweetened chocolate in a double boiler or microwave. Meanwhile, combine the sugar, evaporated milk, butter, vanilla, and salt in a blender; there's no need to blend at this point. If you think your blender might be too small, divide the recipe in half and make in 2 batches. When the chocolate is melted, remove it from the heat and give it a stir. Scrape the hot melted chocolate into the blender. Cover with the lid and blend on high speed until the mixture darkens and is very thick, about 2 minutes. You'll also hear the engine working harder when the frosting is sufficiently thick, and it will appear to be barely moving in the blender. It will not be pourable. Scrape the frosting into a clean bowl and set aside at room temperature. When the frosting is cool, cover the bowl with plastic wrap until the cake is completely cool and ready to frost.

5. To frost the cake: Brush away any loose crumbs from the cake layers. Center 1 layer, top side down, on a flat serving plate. To protect the plate from smears during frosting, slide small strips of foil or parchment under the bottom of the cake to cover the plate. Using a metal spatula or the dull edge of a table knife, spread 1 cup of the frosting evenly over the layer. Place the second layer, top side down, on top of the frosting. Be sure the sides are lined up and then press gently on the layer. Apply a very thin layer of frosting over the entire cake to seal in any crumbs. Spread the remaining frosting over the top and sides of the cake. Garnish the top with coconut or walnuts, if using. The cake is best served at room temperature.

The cake layers can be made in advance and stored at room temperature for up to 2 days, or frozen for up to 3 months. Thaw before using. The entire cake can be prepared, covered, and stored in the fridge for up to 3 days.