Preheat the oven to 150C/300F/Gas 2
Line a baking tin with baking paper. Ideally use a square tin that measures 7", however any baking dish that allows you to get the mixture flattened out to around an inch in depth will work well.
Mix all of the ingredients together in a bowl, ensuring that there are no dry ingredients left showing.
Pour into the baking dish, flatten with the back of a spoon and bake for 30 minutes, or until a skewer comes out clean.
Lift the baking paper out of the tin and place onto a cooling rack until cooled.