Preheat oven to moderate. Grease 19cm x 29cm rectangular slice pan.
Line base and two opposite sides with baking paper
Melt the butter and chocolate in medium saucepan stir over low heat without boiling until mixture is smooth. Cool until just warm
Stir in sugar, egg and essence then sift flour, choc bits, cream and nuts. Spread mixture into prepared pan.
Bake in moderate oven about 30 - 40 minutes. Switch off oven and leave for another 20 minutes. Brownies should be cooked through and moist, but not dry
Stand brownies in pan until it reaches room temperature.
Cut into 24 pieces, dust with sifted cocoa to serve.