Brown hazelnut in the oven or in a frying pan, put in a tissue bag and rub a bag between the palms to get rid of the husk. Beat up white of eggs and gradually pour in sugar and a few drops of lemon juice. Meanwhile, make a nut mixture of finely chopped roasted nuts (leave certain portion for sprinkles), 40 grams vanilla sugar and 40 grams flour. Add this mixture neatly to the egg whites beaten up to stiff peaks. Cover the baking sheet with baking parchment. Lay out two or three round flat cakes, and make even. The amount of cakes depends on the diameter: the thickness of a raw flat cake should be 1.5-2 cm. Bake for 20 minutes at 170 °C, and then at 140-150 °C for about 1 hour and 45 minutes. Leave to cool for one hour in the oven with the door slightly opened. Ideally it must dry nightlong. Make a pastry cream: beat the yolks with sugar powder, warm the milk, pour hot milk into the yolks with sugar, place on a water bath and stir to the state of "strips on a flat beater". Cool and cover with a film. Beat up butter to white and pour in the cooled pastry cream spoon by spoon. Add cognac. Divide the cream into two parts. Cream №1 is just half of our white cream. If you want a classic design, then you need to put 2 tablespoons white cream from the cream №1 into the mini confectionery bags: make the one pink-colored and the other - blue. Make cream №2 from the second part of the white cream. Add cocoa stirred in a small amount of milk, or melted and slightly chilled dark chocolate (100g). You also need cream №3 for the classic design: two tablespoons cream №1 and half of cream №2, i.е. we get mocha color. Refrigerate all the creams in confectionery bags for 30 minutes. Decorate the cake: put the lower cake flat on bottom. Spread 2/3 of cream №1 on it. Put the upper cake flat on up and spread cream №3. Spread the rest of the first cream on the cake sides and sprinkle them with the remaining nuts. Dress the cake with a pink, blue and chocolate cream № 2. You can add wafer roses and flaked almonds.