Coffee and Walnut Cake

This coffee and walnut cake is wonderfully sophisticated. Part of the reason for its delicious appeal is the use of the best-quality ingredients - Californian walnuts and real espresso coffee. Don’t be tempted to substitute instant coffee granules here: the cake will taste much better - and be more indulgent - if you include a cup of real espresso. The coffee and walnut flavours are enhanced when the cake is layered with coffee buttercream and covered in glossy dark chocolate ganache for a