Coffee and walnut cake can be found in every tearoom. Even though it’s old fashioned, it hasn’t fallen out of favour. You can make one cake and decorate it with buttercream or you can make several layers with buttercream in between.
You can make buttercream in several different ways. Italian buttercream is made with Italian meringue, which is made by whipping egg whites together with hot sugar syrup. The meringue is then beaten until it has cooled, after which the butter is added. This buttercream has a very white appearance. For Swiss buttercream, a mixture of egg white and sugar is heated in a bain marie at 71°C (160°F), then the egg whites are whipped and butter is added. The French method isn’t that different: they first make a pâte à bombe by boiling water with sugar at 121°C (250°F). In the meantime, they whip the egg whites, then add the sugar syrup and beat until cold. Subsequently, cubes of butter are added to create a creamy, smooth buttercream. The Germans do it completely differently and make a mousseline cream that consists of 1 part butter and 2 parts pastry cream. There are many more versions, but here I’ve used the simplest, which is the English or American version. This buttercream is not really smooth, but its advantage is the simplicity – anyone can make it.
Put the butter and sugar in a bowl and beat until creamy. Add the eggs, one at a time, and make sure that each egg is completely incorporated before adding the next one. Add a teaspoon of the flour with the last egg to prevent the mixture from separating. Stir in the instant coffee, cocoa, cinnamon and salt.
Carefully fold the remaining flour and the baking powder into the batter so that the volume is retained. Mix in the walnuts, divide the batter between the cake tins and smooth the tops. Firmly tap the tins on the bench to distribute the batter and remove any air bubbles.
Let the cakes rest for 5 minutes before taking them out of the tins, then let them cool further on a wire rack.
For the buttercream, beat the butter in an electric mixer until it turns white; this is an important step. Add the icing sugar, one spoonful at a time, until it is completely absorbed. Finally, add the instant coffee and mix well until the buttercream is fluffy.
To assemble the cake, choose the cake with the smoothest top and set it aside. Spread the other cake with buttercream or use a piping bag fitted with a star nozzle to pipe a pattern over the cake. Place the second cake on top and lightly press down. Decorate the top of the cake with buttercream and walnut halves.
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