1: Blend 100 g rolled oats for a few seconds to obtain a rough oat flour.
2: Put this oat flour, 100 g flour, 100 g butter (cut into small pieces), 50 g caster sugar and 1 egg into the mixing bowl of a food processor.
3: Knead until evenly mixed (about 4 or 5 minutes).
4: Gather the dough together into a slab and wrap in plastic film. Refrigerate for at least 2 hours.
5: Preheat oven to 180°C (360°F). Roll out the dough to a thickness of 3-4mm (a bare ¼"), then cut out circles with a découpoir or an upturned glass. Place these on a baking sheet.
6: Bake for 15-20 minutes. It is important not to overcook them.
Remarks
If you want a more oaty flavour, reduce the quantity of flour by half, and increase the oats by the same amount.