Combine flour, 2 tablespoons sugar, baking powder, and salt in a bowl. Cut in butter with a knife or pastry blender until mixture resembles coarse crumbs. Whisk milk, egg yolk, and 3/4 teaspoon lemon zest in another bowl; stir into crumb mixture until dough is moistened. Turn dough out onto a lightly floured surface and knead 10 turns. Divide dough in half; pat or roll out into a 3/4-inch thick round. Transfer rounds to a baking sheet.