Mix the butter, sugar, baking powder, bicarbonate, cocoa powder, and a pinch of salt with the whisk and incorporate an egg.
Gradually add flour and milk while stirring with the spatula.
Mix until you have a homogeneous mass.
Line an oven tray of about 40 by 27 cm with baking paper and grease the corners with butter.
Spread the dough on the baking tray with a palette knife.
Bake the dough for 9 minutes in a preheated oven at 160°C.
Put the vanilla ice cream with frozen raspberries in the food processor. Stir occasionally with a spatula.
Cut out 2 bases from the brownie dough for the stone baking dish of about 20 x 27 cm.
Place a layer of baked brownie in the stone baking dish. Spread the raspberry ice cream over it and place a second layer of baked brownie on top.
Place the baking dish in the freezer.
Cut into small portions and wrap the bottom part with butter paper so you can easily hold your ice cream sandwich.
Dig in!