Beat the mascarpone, cottage cheese, sugar and milk until you obtain a smooth cream. Separately, whip the cooking cream and then gradually mix them. In a suitable tray, put a small part of the cream. Crush the biscotti on top, pour on eggnog and cream again, then biscotti, and eggnog.
Arrange in this manner until out of products. You can leave the biscotti whole, if desired. Cover the tiramisu with eggnog with the remaining cream and sprinkle it with sifted cocoa. Leave the tiramisu in the refrigerator for a few hours before serving it.
Cut it into pieces and serve it with milk and chocolate syrup.