Dissolve instant coffee in the 1 Tbsp. milk. In a mixer bowl beat the butter with an electric mixer for 30 sec. Beat in 1 1/2c. of the powdered sugar and the melted unsweetened chocolate. Add egg yolks and the dissolved coffee crystals, beating till the mixture is well blended. Add the remaining powdered sugar and additional milk to make a fluffy frosting consistency.
Slice the loaf cake horizontally into 3 layers. Beat together almond paste and the 3 tbsp water. Spread the bottom cake layer with 1/3c of the almond paste mixture. Top with the next cake layer and repeat layering with remaining almond paste mixture and 1/2c. of the frosting. Top with the remaining cake layer. Frost top and sides with the remaining frosting. Sprinkle sliced almonds atop. Store cake, covered, in the fridge.