- 2 cups grated Parmigiano-Reggiano (about 6 ounces)
- 1 stick (8 tablespoons) unsalted butter, softened
- 1large egg yolk
- 1 cup all-purpose flour
- 1/4 teaspoon salt
- 1 1/2 tablespoons fresh thyme leaves
Blend cheese, butter and yolk in a food processor until forms a ball. Add remaining ingredients and pulse until mixture just forms a dough. Form into 2 (8-inch) logs, then wrap in plastic and chill until firm, about 45 minutes.
Preheat oven to 350F with rack in upper and lower thirds. Line 2 large baking sheets with parchment paper, securing edges of parchment to sheets with dabs of butter.
Cut logs into thin slices (1/8-inch thick) and arrange about 1 inch apart on baking sheets. Bake, switching positions of sheets halfway through baking, until golden, 10 to 12 minutes. Immediately transfer crisps to racks to cool.
Make ahead: Dough logs can be chilled up to 1 week. Crisps can be made 3 days ahead and kept in an airtight container separated with parchment at room temperature.