Using a hand mixer and a large bowl, cream together the softened butter, maple syrup. Then beat in the egg and vanilla extract.
Add in the all-purpose flour, oat flour, baking powder, and salt. Mix until combined.
Shape the dough into a disc. Wrap with plastic wrap and place in the fridge to chill for 30 minutes.
After the dough has chilled, preheat the oven to 350°F.
Remove the dough to a clean and floured surface. Roll out the dough very thinly to between ⅛th and ¼ inch. You can also roll the dough out between two pieces of parchment to prevent sticking.
Cut out shapes with cookie cutters and place on a parchment lined baking sheet.
Bake for 10 - 12 minutes.
Remove the baking sheets from the oven and turn the oven off.
Wait 10 minutes.
Turn the oven back on to 225°F and bake for another 10-12 minutes, or until the cookies just start to turn golden on the bottom.
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Notes
Baking time will vary depending on your oven, size of your cookie cutters, and how thinly the dough was rolled out.
You can make your own oat flour. In our experience 1 cup of whole oats will yield about ¾ cup of oat flour. With this ratio in mind, you would need to blend about 2 ⅓ cup of whole oats to get the 2 cups of oat flour needed for this recipe.
If you end up chilling the dough for longer than 30 minutes or overnight, plan to let it rest at room temperature for at least 45 minutes to soften up enough so you can roll it out.