01 - Heat oven to 425°F (220°C). Line a baking sheet with parchment paper.
02 - In a large bowl, whisk together flour, baking powder, salt, pepper, and dry mustard powder.
03 - Add cold cubed butter and rub in with fingertips until mixture resembles coarse breadcrumbs.
04 - Stir in grated cheddar and chives or spring onions if using.
05 - In a small bowl, whisk whole milk and egg together, reserving 1 tablespoon for brushing.
06 - Pour remaining milk and egg mixture into dry ingredients and gently mix with a fork until just combined, avoiding overworking the dough.
07 - Turn dough onto a floured surface and gently pat into a ¾-inch (2 cm) thick round.
08 - Use a 2-inch (5 cm) round cutter to cut scones, re-rolling scraps as needed. Place on prepared baking sheet.
09 - Brush tops with reserved milk-egg mixture. Bake for 12 to 15 minutes until risen and golden.
10 - Let scones cool slightly on a wire rack and serve warm, optionally with butter.