Heat oven to 200C/180C fan/gas 6. Line 2 baking trays with greaseproof baking parchment.
Beat the butter and sugar together in table top mixer until pale and light, then add the egg, flour, oats and a pinch of salt then beat once more.
Stir in the chocolate chips and fudge pieces then dollop rounded dessertspoonfuls of the cookie dough onto your prepared baking trays – you should end up with 12. Gently press pieces of Twix into the top of each mound and bake in the oven for 12-15 mins or until golden brown at the edges.
Leave to cool for a few minutes on the paper then transfer to a wire rack to cool completely. Amazing in ice cream sandwiches!