1. Preheat the oven to 350∞F. Line an 8" x 8" pan with parchment paper and set aside.2. Prepare the crust and topping. In a large mixing bowl, stir together the oat flour, oats, cinnamon, sugar and salt. Stir in the butter until well combined.3. Pat half of the mixture firmly onto the bottom of the prepared pan.4. Bake for 18-22 minutes or until lightly golden brown. The crust will bubble a little during baking.5. Let the crust cool for 5-10 minutes while preparing the filling.6. In a large mixing bowl, stir together all the filling ingredients. Pour evenly over the crust and bake for 12 minutes.7. Remove from the oven and add walnut-sized pieces of the remaining oat mixture over the filling. It will be a very thick layer and some of it will sink a little into the filling. Bake for another 30 minutes or until the filling is golden brown and firm and the middle is set.8. Let cool for 1 hour and serve with whipped cream or maple caramel sauce. Cool completely before covering. Store at room temperature for up to 2 days or in the refrigerator for up to 4 days.