Heat the oven to 220°C (200°C fan). Line a baking tray with baking paper.
Sift the flour, baking powder, salt, mustard powder and cayenne into a large bowl.
Add the cold cubed butter and rub it in with your fingertips until the mixture looks like rough breadcrumbs. Stop while you can still see small flecks of butter — don’t work it smooth.
Stir through the 2 cups of grated cheese.
Make a well in the centre, pour in the milk, and mix with a butter knife just until it comes together into a shaggy dough. It should look untidy. Do not knead it.
Tip onto a lightly floured bench and pat out to about 3 cm thick — thicker than feels right. Cut into 12 rounds or squares, pushing the cutter straight down without twisting.
Sit them on the tray close together, almost touching, so they support each other as they rise. Brush the tops with a little milk and scatter over the extra cheese.
Bake for 12–15 minutes, until well risen and deep golden with browned cheese on top.
Eat warm, split and buttered. They are at their best within an hour of coming out of the oven.