Preheat the oven to 180 C / Gas 4. Grease an 18cm square tin and line with baking parchment.
Cream together the butter and the sugar until pale and fluffy. Sift in the flour and bicarb then add the remainder of the ingredients and mix well. Transfer to the prepared baking tin and lightly press down the top with the back of a spoon.
Bake in the preheated oven for 20 to 25 minutes or until firm and golden brown. Remove from the oven and mark into squares. Allow to cool for 1 hour then remove from the tin and slice into squares and serve.