Start by combining the flour, sugar, baking powder, and salt in a food processor. Add the butter, processing until the mixture resembles coarse crumbs.

Transfer the mixture to a large bowl, creating a well in the center. In a separate bowl, whisk together the egg, lemon juice, vanilla, and milk.

Pour the wet ingredients into the well of the dry ingredients, stirring just enough to form a dough. Be careful not to overmix.

Roll the dough to about 1 inch thick on a lightly floured surface. Cut out biscuits using a 3-inch cutter and place them on a parchment-lined baking sheet.

If using, prepare the egg wash by whisking the egg and water together. Lightly brush the tops of the biscuits with the egg wash, then sprinkle with turbinado sugar.

Bake in a preheated oven at 375°F for about 18 minutes or until the biscuits are a golden brown. Allow them to cool slightly before serving.