Preheat the oven to 180°C / 160°C Fan / Gas 4. Prepare an 8 inch /20 cm square baking tin, lining it with baking parchment and greasing lightly.
Put the butter in a microwave safe jug or bowl with 75 g chocolate. Melt in short bursts of about 15 seconds in the microwave, stirring in between until you can get rid of all the lumps. Do not allow the mixture to get hot.
115 g butter, 75 g dark chocolate
Next, add the sugar, vanilla and egg. Stir it in well.
210 g soft brown sugar, 1 tsp vanilla extract, 1 egg
Sift the cocoa into the jug.
45 g cocoa powder
Add the flour, baking powder and coffee powder. Again, stir in well to combine.
55 g plain flour, ½ tsp baking powder, 1 tsp instant coffee powder
Add the chocolate chips or chopped chocolate. Stir into the batter until evenly distributed.
50 g chopped chocolate (and nuts/fruit if desired)
Transfer the batter to the prepared baking tray and spread it evenly into the corners.
Bake for 25–28 minutes until the crust is papery and the edges slightly risen but the centre still wobbles slightly.
Allow your one bowl chocolate brownies to cool and firm up for at least 20 minutes on a wire rack before you attempt to cut.
Finally, when the bake is cool, you can cut your brownies into squares, ready to serve. I find a 4 x 4 grid of 16 pieces is just right.