Preheat the oven to 350°F. Butter and flour three 8-inch round cake pans or spray with baking spray.
Cake: In a medium-size bowl use a whisk to sift together all purpose flour, baking powder and salt Set aside.
In the bowl of a stand mixer cream together butter, granulated sugar, egg yolks and vanilla extract. Beat on medium speed for 2-3 minutes or until fully combined.
Lower the speed of the mixer adding the sifted dry ingredients alternately with the buttermilk. Stop to scrape the sides of the bowl periodically.
In a separate clean bowl whip the egg whites until stiff peaks form. Fold the egg whites into the cake batter by hand. .
Divide the batter into thirds. Pour 1/3 of the batter (into each) of two cake pans. Stir the coffee granules into the remaining 1/3 batter. Pour into the third pan.
Bake for 25-30 minutes or until a toothpick inserted into the center comes back clean.
Cool in the pans on a wire rack for 10 minutes, then flip from the pans and cool completely.
Coffee Soak: In a small bowl mix together coffee, granulated sugar and coffee syrup. Cool completely.
Filling: In a large bowl use an electric mixer to whip together the mascarpone cheese, 2 1/2 cups powdered sugar, 1/4 cup heavy cream and vanilla extract. Whip until smooth. Keep chilled until using.
Frosting: In a large bowl whip remaining 2 1/2 cups heavy cream with 1 cup powdered sugar on medium-high speed just until stiff peaks form. (Don't overbeat.) Mix 1/3 of the mascarpone filling into the frosting.
Assemble the Layers: Place 1 plain cake layer on a cake stand. Use a skewer to poke holes all over the surface of the cake. Brush with 1/3 (about 3 tablespoons) of the coffee soak. Spread the cake with 1/2 mascarpone filling. Dust with cocoa powder.
Repeat with second layer. This should be the layer with the coffee mixed in. Use a skewer to poke holes all over the cake and brush with 1/4 cup coffee soak. Spread with remaining 1/2 mascarpone filling. Dust with cocoa powder.
Repeat with the third layer, poking holes on the surface and brushing with remaining coffee soak.
Frost the top and sides with the whipped cream mixture. Decorate as desired dusted with cocoa powder and grated chocolate. Chill for at least 4 hours (or overnight) before slicing and serving.
Store in an airtight container well chilled for up to 3 days.