Preheat your oven to 180°C/160°Fan/Gas 4. Grease and line a 30 x 23cm tin with a depth of 4cm.
Put all the ingredients in a large bowl and beat with an electric mixer until the mixture forms a grainy dough.
Put the dough into the prepared tin, using your hands to press the mixture into the corners. Put a layer of greaseproof over the pressed in mixture and smooth with a rolling pin to achieve a nice smooth base.
Put in the oven and bake for 20 minutes or until golden brown and quite firm to the touch.