1. Preheat the oven to 180ºC/350ºF/Gas mark 4. Cream together butter and sugar for the base until light and fluffy. Add the flour and stir until the ingredients are thoroughly mixed. Knead until smooth.
2. Press this dough evenly into a 20cm square tin and prick the surface using a fork. Bake for 25-30 minutes, remove from the oven and leave to cool in the tin.
3. Meanwhile, place the filling ingredients into a saucepan and stir until the sugar has dissolved. Bring to the boil slowly, then cook, stirring continuously for 5-7 minutes. Cool slightly, then pour over the biscuit and leave to set.
4. For the topping, melt dark chocolate in a glass bowl over a pan of simmering water and spread over the caramel. Leave in the fridge until set.
Recipe courtesy of Lyle's Golden Syrup®