Heat oven to 180C/fan 160C/gas 4. Beat in the lactose free butter, sugars, vanilla, cocoa powder and egg until smooth, then stir in three-quarters of both the nuts and remaining chocolate, then the gluten free flour and bicarbonate of soda.
Heap 12 spoonfuls, spaced apart, on 2 baking sheets (don’t spread the mixture). Bake for 12 mins until firm, then leave to cool on the sheets. Can be stored in a tin for up to 3 days.