Preheat oven to 180 degrees C. Blitz the oats to a fine powder in a blender then mix in a large bowl with the wholemeal flour, baking powder, brown sugar and salt.
Add the butter and mix until crumbly. Add the milk and mix to form a smooth dough. Wrap in cling film and pop in fridge to firm up for about 15 minutes.
Remove your dough from the fridge and roll out to around 3mm thickness. It will be very crumbly so you’ll need to be very careful when rolling. Cut out circles of about 6cm diameter – I used a water glass to stamp out the shapes. Decorate with a pattern of your choice then bake in the middle of your oven for about 15 minutes.
When lightly golden but not too brown, remove from the oven and leave to cool on a wire rack. Store in an airtight container.