Add milk and mustard to dry ingredients and mix lightly with a fork until mixture clings together and forms a soft dough. Turn dough out onto a lightly floured surface and knead gently 5 or 6 times. Divide dough in half. Repeat with remaining dough. Place scones one inch apart on prepared pan.
Pierce tops with the tines of a fork.
Brush tops with water and sprinkle with remaining cheese. Bake for 15 to 18 minutes, or until golden brown. In medium bowl, mix baking powder, soda, thyme, salt and 2 cups flour. With pastry blender or 2 knives, cut in butter until it resembles coarse crumbs. Stir in cheese.