Preheat the oven to 350° F (180° C). Whizz all the ingredients together in a food processor, or rub them together with your fingers. Form into a roll, wrap in cling wrap, and put in the fridge for 20 minutes to firm up (this makes cutting the dough easier).
Cut the dough into thin slices and place them on a parchment-lined baking sheet. Cook for 12 to 15 minutes, until golden on top. If you want to add rosemary salt, pound the needles in a
mortar with a pinch of salt and add a small sprinkle onto the sables when they come out of the oven. Cool on a wire rack to let them crisp up.