Pulse cheese with butter in a food processor until combined. Add flour, yolk, and 1/2 teaspoon pepper, then pulse until a dough forms. Roll into a 6-inch log (1 1/2 inches thick). Wrap in parchment paper and chill until firm, at least 1 hour.
Preheat oven to 350°F with rack in middle.
Cut log into 1/4-inch-thick slices and arrange 1 inch apart on a baking sheet. Sprinkle with remaining 1/2 teaspoon pepper. Bake until golden, about 15 minutes. Cool to warm on a rack.