Brownie mixture:
200 g unsalted butter
150 g dark chocolate (good quality)
200 g caster sugar
4 eggs (room temperature)
1/2 tsp vanilla extract
75 g plain flour
25 g cocoa powder

Vanilla frosting:
110 g unsalted butter
250 g icing sugar
1 vanilla pod

Topping:
25 g demerara sugar (more if desired)