Prepare the casserole dish.
Whip the cream and in another bowl, whisk QimiQ and mascarpone until smooth. Add the sugar, stir in the milk and 2 tablespoons of coffee. Fold in the whipped cream.
Pour a cup of coffee with rum into a deep plate (soup plate). Briefly soak biscotti in coffee solution, layer one after the other in the baking dish and then add a layer of cream on top. Layer the biscuits again and the cream on top.
Refrigerate for a few hours and sprinkle with cocoa powder.