Adapted from the Joy the Baker Cookbook
Makes 10-12 biscuits
Preheat oven to 425°F. Prep two baking sheets with parchment.
In a large bowl, whisk flour, sugar, baking powder, cream of tartar, and salt together. In a smaller bowl, whisk together milk, lemon juice, and egg yolk. In a third bowl, whip the egg whites with a whisk until frothy and light, about 5-8 minutes.
Cut the butter into the flour mixture with a pastry cutter (or just your fingers!) and combine until it is the consistency of a coarse meal. Toss in the cheese cubes and rosemary.
Fold the frothy egg whites into the milk mixture. Create a well in the center of the dry ingredients and add the milk mixture, folding the ingredients together with a fork until just combined. The dough will be shaggy.
Dump the ball of dough onto a floured surface and knead for 8-10 minutes. Form the dough into a flattened disk, one to two inches thick. Cut out biscuits, reform the scraps and cut biscuits out of the rest of the dough until you have none left. Arrange the biscuits on the prepared trays and sprinkle with the coarse salt.
Bake 12-15 minutes, until the tops are just golden.