Combine butter, and sugar in large mixing bowl. Cream ingredients together about 2 minutes, until fluffy. Add eggs, one at a time. Add rum and set mixture aside. Sift together flour, baking powder, and salt in another bowl. Fold the flour mixture with the coffee into the butter mixture. Pour the batter into the cake pan. Bake about 90 min. Test with a toothpick in the center. Let the cake cool 20 minutes, and turn onto cake platter. Dust with powdered sugar.