1Preheat oven to 350 degrees F (175 degrees C). Grease and flour 2 - 8 inch pans. Sift together the flour, baking powder, and salt. Set aside. Mix together 4 teaspoons instant coffee, 1/2 cup cocoa powder, and 3/4 cup boiling water; set aside.
2In a large bowl, cream together the butter and sugar until light and fluffy. Beat in the eggs one at a time, then stir in 1 1/2 teaspoons rum. Mix the milk into cooled cocoa mixture, then beat into the batter alternately with the flour mixture. Pour batter into prepared pans.
3Bake in the preheated oven for 35 minutes, or until a toothpick inserted into the center of the cake comes out clean. Allow to cool.
4To make Mocha Chocolate Frosting: Sift together confectioners' sugar and 5 tablespoons cocoa powder; set aside. Dissolve 2 teaspoons instant coffee with 1/3 cup boiling water; set aside. In a medium bowl, cream butter until smooth. Beat in sugar/cocoa mixture. Mix in the vanilla extract and rum. Beat until smooth and creamy. Spread between layers of cooled cake.