Preheat the oven to 200C/180C Fan/Gas 6. Line two baking trays with baking paper.
Sift the flour and baking powder into a large bowl. Add the salt and butter and rub the butter into the flour until the mixture resembles breadcrumbs. Stir in the grated gruyère.
Gradually pour in the milk, stirring with a knife until the mixture comes together to form a rough, soft dough. You might not need all the milk.
Lightly dust a work surface with flour and roll out the dough to 3–4cm/1¼–1½in thick. Cut out discs using a 5–6cm/2–2½in round pastry cutter. Press the offcuts together and re-roll to make as many scones as you can.
Place the scones on the baking trays and lightly brush the tops with a little milk. Scatter over the Parmesan. Bake for 15–20 minutes, until well risen and golden-brown. Cool on a wire rack.
Try not to twist the cutter as this can result in an uneven rise.
If you like, add some chopped fresh herbs, such as chives, thyme leaves or finely chopped rosemary.