1. Preheat oven to 175 C /325 F/Gas 4. Line a swiss roll tin 33cms/13" x 23cms/9" with baking parchment or greaseproof paper.
2. Put the first 5 Ingredients into a mixing bowl and mix well.
3. Pour over the melted butter or margarine. And mix until all the dry Ingredients are moistened.
4. Transfer to the prepared tin. Press out evenly in the tin, a spoon dipped in water helps to do this!
5. Bake for 25 minutes approx. until firm to the touch when gently pressed.
6. Remove from oven and allow to cool.
7. Turn onto wire tray and allow to get cold.
8. Meanwhile, melt the chocolate and butter and stir to combine. Spread over the baked slab, shake on the Sprinkles.
9. When 'set' cut into squares. Store in an airtight tin.

Note: Size of Mug does not matter, once same size is used for all the Ingredients!!