Preheat your oven to 170°C (340°F)/fan 150°C (300°F)/gas mark 3½ and line a large baking tray with baking parchment.
In a large mixing bowl, combine the flour, mustard powder, sugar, and salt.
Add the cold, chopped butter and rub it in with your fingertips until the mixture resembles fine breadcrumbs.
Stir the grated Cheddar cheese into the flour mixture, then make a well in the centre.
Crack the eggs into a measuring jug and add enough milk to reach the 225ml (7.6 fl oz) mark.
Add the fresh sage leaves and sunflower oil, then blitz with a hand-held blender until combined.
Pour the wet mixture into the well of the dry . Use a knife to gently bring everything together to form a soft, slightly sticky dough.
Do not overmix.
Tip the dough onto a lightly floured surface. Gently roll it out to a 2cm thickness, aiming for a 20cm square shape.
Using a sharp, floured knife, cut the square into four smaller squares, then cut each one diagonally to create eight triangles.
Carefully place the scones on your prepared baking tray, leaving a little space between them.
Brush the tops lightly with a little milk for a golden finish.
Bake for 12–15 minutes, or until well-risen and golden brown. You may want to rotate the tray halfway through for an even bake.
Transfer the warm scones to a wire rack to cool for 10 minutes before serving. They are best enjoyed warm with a generous spoonful of homemade apple chutney.
Keep your butter cold! Cold butter creates steam pockets as it bakes, which is the secret to a light, flaky texture.
