In the bowl where you're going to mix the batter later add butter in cubes, sugar and dark chocolate. Put it on a bain marie making sure that the water doesn't touch the bottom of the bowl.
Once everything is melted together give it a mix, take off the heat and wait for it to be warm.
Add the vanilla essence and 1 egg at a time until fully incorporated with an electric mixer. Mix for a few minutes on high or by hand about 75 times.
Add the flour and salt and mix on high speed for a few extra minutes. It's these intervals of mixing that will give us the paper texture on top.
Line with baking paper a 20x20cm mould and fill with the dough.
Lay the raspberries on top of the dough.
Take to a preheated oven at 180C for 20-30min or until the tip of a knife comes out with a bit of cooked yet moist dough.