Preheat the oven to 180C.
In a heavy saucepan, put both chocolates, the butter and sugar. Melt slowly over a very low heat, stirring regularly.
Remove from the heat and allow to cool for 10 minutes.
Add the eggs and flour and beat until very smooth and totally combined.
Line a small roasting tin (about 9" square - see tips above) with baking paper.
Pour in half of the batter, smooth out.
Sit the chocolates on top and pour over the rest of the batter, smoothing out.
Bake in the oven for 20 minutes.
Remove from the oven and allow to cool fully before cutting into pieces.
Prep time: 15 minutes
Cook time: 20 minutes
75g milk chocolate chunks
75g dark chocolate chunks
125g unsalted butter
150g soft light brown sugar
100g self-raising flour
200g assorted chocolate toppings