Preheat the oven to 190C/375F/gas 5. Pulse the flours, xylitol and salt a few times in a food processor until combined. Add the cubed butter and pulse again for 30 secs or so until the mixture resembles lots of different sized breadcrumbs (the butter should be incorporated but not completely - there should be some clumps). Add the egg and pulse until the dough just starts to come together (if it doesn't, add a few teaspoons of cold water one at a time until it does). Mould the dough together with your hands to forma ball, flatten into a disc and wrap in cling film. Chill in the fridge for 30 mins.

Roll out the dough as thin as you dare and cut out cookies with cutters. Place on a baking tray lined with baking paper and bake for 15-20 mins, until golden round the edges. Transfer to a cooling rack until completely cool.

If doing the drizzle, melt the chocolate in the microwave until smooth, then drizzle with a teaspoon over the cookies.