Preheat the oven to 220°C. Line a baking tray with baking paper.
Sift the flour (3 cups), baking powder (3 tsp) and salt (¼ tsp) into a bowl. Add grated cheese (¾ cup), cayenne pepper (¼ tsp) and mustard powder (¼ tsp) to the mixture. Rub in the butter (75 g) with your fingertips until the mixture resembles fine breadcrumbs.
Add the milk (1¼ cups) and quickly mix with a round-bladed table knife to a soft dough. For light and tender scones the mixture should be quite soft and a little sticky. Scrape the dough onto the floured baking tray and flour the top.
Working quickly, pat the dough out to 2cm thickness. With a floured knife, cut it into 12 even-sized pieces, then separate the scones to allow 2cm space between them. Brush the tops with milk.
Before baking, top each scone with a little more grated cheese. Bake for 10 minutes or until golden brown. Place on a wire rack to cool, wrapped in a clean tea towel to keep them soft.