To prepare a triple hazelnut cake with chocolate buttercream icing recipe, first you need to prepare the cake. First, you'll need: 3 tablespoons butter, 1 tablespoon sugar, and 1 teaspoon vanilla extract. Then, mix the butter and sugar together until they're light and fluffy. Next, add the vanilla and the egg yolks. Finally, beat the mixture with an electric mixer until it's fluffy and light. Pour the batter into the greased and floured cake pan and bake for 35 to 40 minutes, or until the toothpick inserted in the center comes out clean. Let the cakes cool for 10 minutes before removing them from the pan.