Place the oats and the rosemary in a food processor and process until they start to break down and the mixture resembles breadcrumbs.
Add the flour, baking powder and salt and blitz again.
Add the butter and process until it is mixed in, then pour in the milk while the machine is running and process until the dough comes together in a ball.
Turn out onto a lightly floured work surface and roll out to a thickness of about 4–5 mm (¼ inch). Cut out 20–24 rounds using a 4–5 cm (2 inch) cutter, rerolling as necessary, and place on a baking sheet.
Bake in a preheated oven, 190˚C (375˚F), Gas Mark 5, for 12–15 minutes until just starting to turn golden at the edges.
Cool on a wire rack and serve with cheese and apples. Store in an airtight container.