THIS IS A LIGHT vanilla cake with an irresistible coffee buttercream. As with most cakes made with génoise and buttercream, it can be made several days or even weeks ahead (and it freezes well).
Make a light coffee syrup: In a small bowl, combine the boiling water, sugar, and instant coffee. Stir to dissolve.
Using a serrated knife, cut the cake into two layers. Turn the top layer cut side up on the cake rack. Using a pastry brush, moisten both layers with the syrup. (Several tablespoons will remain when mak