Easy microwaved coffee cake

Grease a 13 x 22 x 5 cm microwaveproof dish or glass bowl with margarine.
Place 50 g butter with the brown sugar, self-raising flour, egg, coffee granules and milk in a mixing bowl.
Beat for 1 minute or until the mixture is smooth and well blended. Spoon the batter into the prepared dish.
Microwave for 4 minutes on 100 per cent power, turning the bowl slightly at one-minute intervals. Leave the mixture to stand for 5 minutes.
Blend the breakfast cereal in a glass bowl with 50 g butter and microwave for one minute.
Stir until the butter has melted and spoon the mixture onto the top of the cake.
Cool and cut into squares before serving. (The crust is very crumbly.)
Serve with custard or ice cream.