Preheat oven to 425 degrees F (220 degrees C). Line a baking sheet with parchment paper.
Sift the flour, cream of tartar, baking soda and salt into a bowl.
Rub in the butter until the mixture resembles fine breadcrumbs. Stir in the sugar and enough milk to mix to a soft dough.
Turn onto a floured surface, knead lightly and roll out to a 3/4-inch thickness. Cut into 2-inch rounds and place on the prepared baking sheet. Brush with milk to glaze.
Bake at 425 degrees F (220 degrees C) for 10 minutes then cool on a wire rack. Serve with butter or clotted cream and jam.
