Melt the dark chocolate in a heatproof bowl over a saucepan of boiling water.
Stir through half the chocolate chips/dark chocolate pieces and 3 to 4 strawberries or half the raspberries.
Pour the mix into the brownie tin and top with the leftover strawberry slices or remaining raspberries and chocolate chips/dark chocolate pieces. It is really effective to reserve 16 slices/raspberries and put a slice/berry on each piece so that everyone will get a slice of strawberry or berry on their brownie.
Consume within 2-3 days.