Makes a 18×24cm tin of brownies
Preheat the oven to 180°C fan.
Roughly chop the dark and milk chocolate and put in a saucepan with the butter. Melt in a bain marie (by putting the saucepan in a larger saucepan with boiling water and gently melting it all while stirring).
Put the sugar, vanilla sugar and eggs into a bowl. Beat until it becomes pale, then add the melted chocolate, while still beating. Fold through the flour with a good pinch of salt.
Line the bottom of a brownie tin measuring approximately 18×24 cm with baking paper. Pour the brownie mix into the tin and even out with a spatula. Drizzle over the tahini and, using a knife, cut swirls into the brownie batter so that the tahini and the batter mix a bit.
Bake in the preheated oven for 35 minutes.
Let the brownie completely cool down before turning out of the tin and cutting out heart-shaped brownies with a cookie cutter.