Ingredients
110g plain chocolate, broken into pieces
110g butter
110g plain flour sifted
225g caster sugar
2 eggs, beaten
1/2 teaspoon baking powder
Optional: chocolate chunks (we prefer white chocolate)/walnuts etc...
The original recipe that this came from says this amount feeds 8-10 people. They did not base that estimate on my capacity for chocolate. Doubling the quantities yields a decent amount suitable for sharing at conventions.
Method
Put the chocolate & butter in a heatproof bowl. Stand the bowl over a saucepan of gently simmering water until it melts. Chocolate burns really easily so never melt it over a direct heat & make sure that the bottom of the bowl doesn't touch the water in the saucepan.
When melted take the bowl off the heat & stir in all the other ingredients. The more consistent your mixture is the better the results.
Spread the mixture into a greased 18*28cm (7*11 inches in old money) baking tray & bake in a preheated oven at 180°C/350°F/Gas 4 for 30 minutes. Don't overcook it or you will lose the nice fluffy texture. The best way to tell whether it is done or not is to gently poke a knife into the centre then pull it out. If the blade has gooey chocolate on it then it needs a bit more baking, if it's clean it's done.
Leave it to cool in the baking tray for 10 minutes (it will sink a little bit). Cut into pieces as desired & leave to cool on a wire rack.