Add the oats, milk, flax, maple syrup, vanilla, cinnamon, baking powder, and salt to your blender and puree until smooth. Pour into a greased 8x8" baking dish.
Drop cookie butter by the teaspoon all over the batter.
Bake for 25 to 30 minutes, or until a toothpick inserted into the center comes out clean. When you do the toothpick test, make sure you aren't stabbing in a spot that has cookie butter in it.
Remove from the oven and let it cool for 10 to 15 minutes. Meanwhile, warm up some more cookie butter in the microwave, if using, and drizzle it all over the top. Sprinkle on crushed Biscoff cookies or stick cookie pieces right into the baked oats. Or do both! Slice and serve.
Video
Notes
Nutritional information doesn't include optional toppings.Store leftovers in the baking pan (covered in foil) or slice and store individual pieces in a covered container. Serve cold, at room temperature, or warmed in the microwave.