Heat oven to 350 degrees F. Grease a 15x10-1/2x1-inch jelly-roll pan. Line with parchment or waxed paper. Grease and flour paper.
Spread whole almonds in a single layer on a cookie sheet and bake 8 to 10 minutes or until golden. Cool completely on wire rack.
Process cooled almonds, cake flour, 1/4 cup of the sugar, baking powder, and 1/4 teaspoon of the salt in a food processor, until almonds are very finely ground. Set aside.
Beat 1/4 cup of the sugar, the 8 egg yolks, and 2 tablespoons coffee powder in a large bowl on medium-high speed of electric mixer 5 minutes, scraping bowl occasionally, until thick and coffee is dissolved. Beat the 1/4 cup melted butter into batter in a thin, steady stream, until blended.
Beat egg whites and remaining 1/4 teaspoon salt in another large bowl with clean beaters on medium-high speed to soft peaks. Gradually beat in remaining 1/2 cup sugar just to stiff peaks (do not overbeat). Fold a large spoonful of the whites into yolk mixture. Fold in half of the almond mixture just until blended. Fold in half of the whites just until blended. Repeat with remaining almond mixture and whites, folding just until no streaks of white remain.
Pour batter and gently spread evenly into prepared pan. Bake 22 to 23 minutes or until top springs back when pressed gently with fingertip. Immediately invert cake onto a large wire rack; remove pan and peel off parchment or waxed paper. Place another large wire rack over top; invert and cool completely.
Beat the 1-1/2 cups butter in another large bowl on medium-high speed of electric mixer until light and fluffy, scraping bowl occasionally. With mixer on medium speed, gradually beat in egg yolk mixture, scraping bowl occasionally, until blended and buttercream is light and fluffy.
To assemble, transfer cake to a large cutting board. Cut lengthwise with serrated knife into thirds. Transfer one layer to a serving platter. Spread top with 1/2 cup of the Coffee Buttercream Frosting. Top with another layer and spread top with 1/2 cup of the Coffee Buttercream Frosting. Top with remaining layer; spread sides, ends and top with remaining Coffee Buttercream Frosting. Place melted chocolate in small plastic storage bag; snip small hole in one corner. Drizzle chocolate over top of cake. Press Sugared Almonds onto ends and sides of cake. Cut crosswise with serrated knife into 16 slices. Makes 16 servings.
Coffee Buttercream Frosting
Whisk the sugar and cornstarch together in heavy medium saucepan, until blended. Whisk in coffee powder and the egg yolks until combined. Whisk in milk and vanilla. Cook over medium-low heat, stirring constantly with a heatproof rubber spatula, until thickened, about 2 minutes (do not boil). Pour custard into large bowl and beat on medium speed of electric mixer until slightly thickened and completely cool, about 5 minutes. Set bowl aside.
Beat the butter in another large bowl on medium-high speed of electric mixer until light and fluffy, scraping bowl occasionally. With mixer on medium speed, gradually beat in egg yolk mixture, scraping bowl occasionally, until blended and buttercream is light and fluffy.
Reduce oven temperature to 325 degrees F. Grease a large cookie sheet. Toss sliced almonds, sugar, and the water in medium bowl, until evenly coated. Spread on prepared sheet. Bake 12 to 15 minutes or until lightly browned. Immediately loosen almonds with a wide spatula. Cool completely on sheet, then break up almonds slightly to separate.