Cut off the top of the sponge cake, break it into pieces, put it on a baking sheet, send it to the oven and lightly dry / fry until golden brown. Then the biscuit pieces are crushed into crumbs using a shredder. Then cut the sponge cake into several cakes (2-3-4).
For the cream:
Mix boiled condensed milk (3 tbsp.l.) and sour cream (180 gr.) in a bowl. Whisk the mixture. Lubricate the cakes with the prepared cream. Sprinkle the edges and partially the top of the cake in the form of a side with the prepared biscuit crumbs. You can prepare your favorite cream as desired.