Preheat the oven to 200 C or 400 F, grease a baking tray or use a baking sheet.
Thoroughly mix the oat flour with the sugar, baking powder and salt. Then rub in the butter until it resembles course sand.
Add a bit of water to form the mixture into a stiff dough, knead lightly until it’s pliable.
Flour your work surface and roll the dough out so that it is about 3 mm thin.
Cut out your biscuits with a cutter and place on your baking sheet/tray.
Bake in the preheated oven for 10 to 15 minutes. After they are done baking let them cool on a wire rack.
Place into an airtight container when fully cooled, they should keep for 3 to 4 days.
Notes
You don't need to buy oat flour, you can quite easily just use plain rolled oats and stick them in a blender. And voila you have just made some homemade oat flour, it works perfectly and it's what I do whenever I want oat flour.