Preheat the oven to 200°C/gas mark 6. Lightly grease a baking sheet. Sift the flour, baking powder and a pinch of salt into a bowl.
Rub in the butter using your fingertips. Stir in 80g Gruyère along with the Dijon mustard, thyme and cayenne pepper. Gradually pour in the milk, bringing the mixture together with a knife to form a dough.
Tip on to a lightly floured surface and roll out to a thickness of 2cm. Use a 5cm pastry cutter to cut out rounds. Put on the baking sheet and sprinkle the remaining Gruyère over the tops. Bake for 12-15 minutes until risen and golden.