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 making an 8-inch cake.)
Spread a thin, even layer of coffee buttercream over the bottom layer. Replace the top layer.
Ice the top and sides of the cake with a thin layer of the remaining buttercream. If you have a pastry bag and starred decoration tube, you can use them to make a decorative border on top of the cake.
Scoop up the toasted almonds in your hand and press them gently onto the sides of the cake. Refrigerate or freeze the cake on the rack. When the icing is firm, transfer the cake to a doilied serving plate. (The cake will keep refrigerated for several days, or can be frozen for several weeks. Let the cake return to room temperature before serving.)