240 gmplain flour½ tspcayenne pepper, or to taste, plus extra for dusting160 gmunsalted butter, chilled2 tbspsparkling mineral water, chilled80 gmfinely grated Grana Padano or sharp cheddar80 gmcoarsely grated GruyèreTo serve:green olives, such as picholine
Mix flour, cayenne pepper, 2 tsp sea salt flakes and 1 tsp freshly ground black pepper in a large bowl. Grate chilled butter over and rub with your fingertips to form coarse crumbs. Add mineral water and knead to just combine, then knead in cheeses, taking care to work lightly (don’t overmix). Roll into a 34cm-long cylinder, wrap in plastic wrap and refrigerate until firm (30 minutes-1 hour).
Preheat oven to 200C. Slice dough into 1cm-thick rounds, place on 2 oven trays lined with baking paper and press each with a fork to lightly flatten. Season with a few turns of freshly ground pepper and a light dusting of cayenne. Bake, swapping trays halfway through cooking, until golden and aromatic (10-15 minutes). Cool slightly on trays, then cool on a wire rack and serve with green olives. Biscuits will keep in an airtight container for 2 days.