These crunchy biscuits are a twist on a classic Italian recipe. Ring the changes by substituting the pistachios with other chopped nuts.
Preheat the oven to 160C/350F/Gas 4.
Combine all the dry ingredients in a bowl, add the egg yolk and vanilla and mix well to form a dough.
Lightly knead the dough on a floured work surface until smooth then shape into a log and place on a baking tray lined with parchment.
Bake for 25 minutes, allow to cool, then cut into slices about 1cm/½in thick. Place slices onto the baking tray and bake again for 5-10 minutes.
