Preheat the oven to 200˚C fan / 220˚C / 392˚F convection / 430˚F
Line a baking tray with baking paper / baking parchment.
In a large mixing bowl, combine the flour with the baking powder.
Add the butter, then lightly rub it in to the flour with your fingertips until the mixture resembles breadcrumbs.
Stir through the grated cheese.
Mix the milk, water and mustard together in a small bowl.
Pour the wet ingredients in to the flour mixture and stir lightly until the mixture just comes together. You don't want to over mix the dough as this will result in heavy scones.
Place the scone dough on a lightly floured surface and roll out with a rolling pin to 3cm (1.2 inch) thick.
Cut out rounds using a 58mm (2 ¼ inch) scone cutter or cookie cutter, and place on the lined baking tray, almost touching. Don't twist the cutter in the dough - just press down and bring up. The twisting motion can prevent the scones from rising as well.
Sprinkle over a little extra grated cheese (this is optional but recommended!), then place in the preheated oven.
Bake for 12-15 minutes, until the scones have risen and are lightly golden.
Cool on a wire rack.