Cover a 9″ (23 cm) diameter baking form with baking paper. Arrange the biscotti at the base of it.
Pour the melted chocolate, espresso and liqueur to the mascarpone in the blender and blend. Beat the egg whites to a stiff snow.
Mix 2/3 of the chocolate mixture with 1/3 of the egg white mixture. Pour the chocolate mixture on top of the biscotti base. Pour on the egg white mixture on top and finish off with the final chocolate part. Bake in a preheated 392°F (200 °C) oven for 45 min. Cool and serve.