Step 1First, prepare the brownie base. Preheat the oven to 175 °C/ 350 °F (fan assisted), or 195 °C/ 380 °F (conventional). Break the chocolate into small pieces and add to a heatproof bowl with the butter. Place over a pan filled with simmering water and make sure the water doesn’t touch the bowl: only the steam should heat the bowl. Slowly melt while stirring.