Mix all the ingredients in a large tall bowl. Microwave for 4 minutes and stir well. Microwave for another 4 minutes (check periodically to make sure the mixture does not spill over).
Stir well again and microwave for another 3 minutes. Pour the mixture into a greased flat pan, leave to set. Once it is set, cut into small pieces.
(Note: Microwave strength/power vary on each machine. Try to use lower power level if possible to prevent spills.)