Preheat oven to 350F and line a 8x8inch pan with parchment paper, spray paper with nonstick cooking spray.
Crust + crumble: In a large bowl, mix together the oat flour, oats, coconut sugar, cinnamon, baking soda and salt. Add in melted butter and vanilla and stir until crumble forms and dough begins to clump together. Spread about 1 2/3 cups of the dough into the pan and place the remaining mixture into the fridge. Evenly press dough into pan.
Apple filling: melt butter in a large skillet or pot over medium heat. Add the apple slices and stir to coat the apples in butter. Add in maple syrup, cinnamon, allspice and lower heat to medium low and allow to cook for 5-7min or until apples begin to soften. Stir in vanilla and cornstarch and cook over low heat for an additional 3-5min until the sauce thickens up. Remove from heat and pour mixture over the crust and spread evenly. Take the remaining dough mixture out of fridge (should have clumped together into crumbles) and sprinkle on top of the apple filling.
Bake for 30-35min or until top is golden. Let bars cool COMPLETELY in the pan on a wire rack before cutting into and serving. Serve with vanilla ice cream and enjoy!
