Whip eggs and sugar on high speed for 3 minutes. (A stand mixer is very useful for this sort of technique.) Place the beaten eggs over a pot of simmering water, being careful not to let the bowl touch the water. Stir eggs constantly until warmed by the steam.
When the egg and sugar mixture feels warm to the touch (a bit over 100 degrees), mix again on high speed until tripled in volume, 5 minutes or more.
Sift together the cake flour and the cocoa. Gently fold dry ingredients into the egg and sugar mixture until thoroughly blended.
Heat oven to 350° F. Butter a 10-inch cake pan. Line with a round of parchment paper, and butter the paper. Dust with flour, and tap out excess. Pour the genoise batter into the cake pan, and bake for 40 to 45 minutes, until cake tests done and sides pull slightly away from sides of the pan. Transfer to rack to cool.
Stir together the coffee and the instant coffee in a small pot, and bring to a boil. Stir until instant is dissolved. Remove from heat, and stir in chocolate chips until smooth. Cool.
Whip butter until light. Add yolks one at a time, beating until smooth. Slowly add sifted powdered sugar. Then add the mocha mixture. Beat until blended.
Whip cream until foamy. Gradually add powdered sugar while continuing to whip to stiff peaks. Fold in Kahlua to taste. Chill.
Carefully slice the genoise into two equal layers. Sprinkle the bottom half with 2 tablespoons Kahlua to moisten the cake. Spread the Kahlua cream filling on the bottom cake half. Sprinkle the cut side of the top half with 2 tablespoons Kahlua and place top layer on cream filling. Frost top and sides of cake with the mocha buttercream. Sift 1/2 cup powdered sugar over top of cake. Press toasted almonds onto sides of cake.Makes 8 to 10 Source: