Preheat oven to 400 F. In a large bowl, whisk together flour, salt, sugar, baking powder, and cream of tartar. Cut butter into the mixture with a pastry blender until crumbly.
Pour in milk, mix until combined. Pat dough out onto a floured surface. Cut out biscuits with a round cookie cutter. Place biscuits onto a greased baking sheet. Bake for 15 minutes.