1.Preheat oven to 200°C (180°C fan-forced). Grease 8 holes of a 12-hole (1/3 cup/80ml) muffin pan, line bases with rounds of baking paper.
2.In a medium heavy-based saucepan, combine butter, chocolate and sugar. Stir over a low heat until smooth.
3.Transfer to a bowl and stir in egg, essence, sifted flour and cocoa, then extra chocolate. Divide mixture among the prepared 8 muffin- pan holes. Sprinkle with nuts. Bake for about 20 minutes.
Brownies can be made three days ahead.Note