We strongly recommend measuring the flour and cheese by weight. We like the flavor of cheddar cheese that's been aged 16 to 18 months, but any block of extra-sharp cheddar will work. Yellow cheddar adds contrasting color, but white cheddar can be used. The scones are best enjoyed warm.

Adjust oven rack to middle position and heat oven to 400 degrees. Line rimmed baking sheet with parchment paper. Pulse flour, Parmesan, baking powder, salt, and mustard in food processor until combined, about 5 pulses. Add butter and pulse until butter is reduced to mostly pea-size pieces, 25 to 30 pulses. Transfer mixture to large bowl. Add cheddar and toss until coated with flour mixture.

Whisk milk and egg together in small bowl. Set aside 1 tablespoon milk mixture. Add remaining milk mixture to flour mixture and, using rubber spatula, fold until no dry bits of flour remain.

Transfer dough to well-floured counter. With your floured hands, knead dough until cohesive, 4 to 6 times, dusting counter with more flour as needed. Using your floured hands, pat dough into 7-inch round, about ¾ inch thick. Using floured bench scraper or sharp knife, cut dough into 8 wedges, recoating bench scraper with flour if it begins to stick.

Arrange scones on prepared sheet, spacing them at least 1 inch apart. Brush tops of scones with reserved milk mixture. Bake until risen and golden brown, 15 to 18 minutes, rotating sheet halfway through baking. Let scones cool on sheet for 10 minutes. Serve scones warm or at room temperature.

An Extra-Cheesy Formula