Preheat the oven to 350°F. Line an 8x8 inch pan with parchment paper and set aside.
In a large bowl, whisk together the oats, oat flour, whole wheat flour, baking soda, cinnamon, salt and brown sugar. Add the apples and stir to combine.
In a small bowl, whisk together the applesauce, vanilla and buttermilk until smooth. Add this to the apple mixture and stir until everything is evenly moistened. Spoon the batter into the prepared pan (it will be thick) and smooth it into an even layer.
Bake for 30-35 minutes until a toothpick inserted in the center comes out clean and the squares are golden brown. Allow to cool in the pan then lift out the parchment paper and slice into squares.
For the Glaze:
In a small saucepan over medium heat, melt the butter.
Add the powdered sugar and maple syrup and stir until the glaze is smooth. If necessary add 1/2 to 1 tablespoon of water to thin it out.
Drizzle over the cooled oatmeal squares.
Store the squares in an airtight container at room temperature for 4-5 days, or freeze for up to 3 months.
If you don’t have oat flour, you can easily make it by grinding regular oats in a food processor for a couple minutes. Just be sure to measure the flour after grinding, not before.
If you want these to be even healthier, you can omit the glaze.
The buttermilk can be subbed with regular milk if you don’t have any.