Preheat the oven to 180 celsius/ fan 160 celsius/ Gas 4. Grease the cake tin and cut a piece of non stick greaseproof and baking paper to the base of the tin
Break the chocolate bar into chunks and put into a small saucepan with the butter and melt over a gentle heat, stirring every now and then.
Take off the heat and leave to cool slightly
Put the flour, cocoa and sugar into a bowl, add the eggs, cooled chocolate and vanilla extract and beat together
Spoon into the tin and bake for 15-17 minutes( the top should be crisp and cooked but the inside should be still be gooey- don't be tempted to overcook them)
Leave then brownies to cool in the tin. Once cooled, cut in half lengthways and then cut into 16 pieces
Tip
You can put some orange and chilli in it but you have to use dark chocolate or else it doesn't taste nice