This coffee and walnut cake is inspired by the classic British dessert, though I’ve skipped the standard American buttercream and instead gone extra-silky with Swiss meringue buttercream that’s laced with a touch of cocoa powder. (Not sure about the difference? Jump to this guide to types of frosting.) The cake layers, flavored with finely ground toasted walnuts, are surprisingly sponge-like and light. The walnuts and the coffee, in the form of instant espresso powder, give a pleasantly bitter edge to this otherwise rich and sweet cake.
This recipe makes a generous batch of mocha buttercream to allow for the most ornate of decorations; any leftovers can be frozen in an airtight container for up to three months. (Bring to room temperature and beat again before using.) If the buttercream ever looks split while you’re making it, with fat separating from the meringue, keep beating on high speed and it will smooth out soon enough. If it stiffens to the point that the butter will not incorporate, place the bowl back over the simmering water for a few seconds to let the mixture reheat, then continue beating as before, adding the remaining butter a tablespoon at a time.
For those who would like to lean into the deeper tannic notes of the walnuts and coffee, heat ¼ cup sugar and 3 Tbsp. water in a small saucepan, stirring until the sugar dissolves. Stir in 1 Tbsp. amaro and ½ tsp. instant espresso powder. Dab syrup on the cut layers of the cake with a pastry brush before frosting.