Preheat your oven to 350F.
Whisk together the oat flour, baking powder, cream of tartar and salt.
In another bowl whisk together the butter, syrup, egg until combined.
Add the wet ingredients to the dry and pour into six muffin liners. Due to the oat flour, these will be very tender, so the muffin liners are needed!
Top with cinnamon sugar and bake at 350F for 20-25 minutes.
Serve warm!