1. Preheat the oven at 180 degrees C /356 F/. Grease and flour 2 cake pans 10 inch long.
2. In a large bowl combine flour, egg yolks, cocoa powder, baking powder, sugar, vegetable oil, and buttermilk. Beat with an electric mixer on medium speed. Dissolve instant coffee in hot water and add it to a mixing bowl. Beat for 2 more minutes until blended.
3. Pour mixture into prepared cake pans and bake for 30 min. Remove from the oven and set aside to cool.
4. Meanwhile prepare Mocha frosting. In a large mixing bowl combine softened butter and powdered sugar and beat with electric mixer until creamy. Add cocoa powder, instant coffee and vanilla extract.
5. Beat with the mixer for 3 min until mixture is smooth and fluffy. Put the frosting in the fridge for 40 min to make it more firm.
6. Spread frosting evenly over the cake layer and decorate with grated chocolate on top.
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