- Preheat oven to 325F. Butter 2 9-in. round cake pans and line bottoms with parchment. Sift flour with cocoa, baking soda, baking powder and salt into a medium-sized bowl. Stir until mixed. Beat butter with sugars in a large bowl, using an electric mixer on medium, for 3 min. Add eggs, one at a time, beating well and scraping down sides of bowl after each addition. Beat in vanilla. Reduce speed and beat one-third of flour mixture into butter mixture, then add half the buttermilk. Repeat additions, scraping down sides until well mixed. Divide batter evenly between pans and smooth tops.
- Bake in centre of oven until a cake tester inserted in centre of cakes comes out clean, 25 to 30 min. Cool in pans on a rack for 10 min. Run a knife around inside edge of each pan, then turn cakes out onto rack. Remove parchment. Let cool completely, about 1 hour. Meanwhile, prepare icing.
- Beat butter for icing in a large bowl, using an electric mixer on medium, until creamy, 1 min. Add melted chocolate, vanilla, salt and 1 cup icing sugar. Beat for 1 min. With mixer on medium-low, add remaining sugar in 3 parts, alternating with remaining liquids (milk and coffee) and ending with sugar. Beat on medium-high, scraping down sides of bowl as needed, until fluffy and smooth, 1 to 2 min.
- Assemble by slicing each cake in half horizontally. Place one layer on a large plate or cake stand, cut-side down. Lay short strips of parchment paper under edges of cake to protect the plate. Spread cake with 3/4 cup icing, right to edge. Top with another cake layer, cut-side down. Repeat icing and layering with remaining cake layers. Then spread remaining icing on top and around sides of cake, smoothing or swirling surface. Cake can be refrigerated up to 1 hour to firm icing before serving.
Substitute more milk for coffee for a kid-friendly variation. To make ahead of time, gently place several toothpicks in top of iced cake, then loosely cover with plastic wrap, sealing to the edge of plate. Cake will keep well, covered, at room temperature, up to 2 days.
3 Steps to Perfection!
1. Even Layers
Cut uniform layers by placing toothpicks horizontally at each cake’s midpoint. Then use a long serrated knife to slice just above them.
2. Clean Stand
Place the first layer on a cake stand. Slide strips of parchment paper under the cake. Use lots of frosting in between layers.
3. Smooth & Swirly
Use a thin palette knife to create a swirly top. Drag the same knife along cake edges for smooth sides. Remove parchment strips.