Preheat the oven to 170'C.
Melt the butter and the chocolate in a bowl over a pan of simmering water.
Whisk the eggs and the sugar together until doubled in volume. Gently fold in the melted chocolate and the flour.
Butter the silicone muffin moulds and dust with flour. Pour the mixture into the moulds until they are 3/4 full. Transfer to the oven and cook for 10 minutes.
Remove from the moulds and serve when cool.
«Add a few chopped walnuts, pecans, hazelnuts or even pistachios to the brownie mixture to give a little crunch to these brownies.»