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. Once doubled in volume, gently fold in the melted chocolate, the flour, cocoa powder and the chopped hazelnuts.
Butter silicone muffin moulds and dust with flour. Pour the brownie mixture into the moulds so that they are 3/4 and cook in the oven for 10-12 minutes.
Remove from the moulds and serve when cool.
«Extend or reduce the cooking time depending on how gooey you like your brownies. Serve warm with cream, ice cream or caramel for an indulgent dessert.»