1. Streusel topping: Mix the ingredients together until it forms a chunky crumb and set aside.
2. Preheat oven to 350ºF. Grease a 9×9 pie dish or baking dish. Set aside.
3. Apple layer: Place the thinly sliced apples in a bowl and toss with the oat flour. Add the maple syrup, ground cinnamon, ground nutmeg, and vanilla extract and combine using tongs.
4. Fill 1/3 cup with the streusel mixture then add to the apple mixture and mix together. This helps absorb some of the extra moisture from the maple syrup.
5. Place the apple mixture into the prepared pan. There is probably maple syrup at the bottom of the bowl – be sure to pour that over top of the apples.
6. Evenly spread the remaining streusel topping over the apples.
7. Bake for 40-50 minutes, or until the topping is golden brown and the filling is bubbling.
8. Remove from the oven and let cool for at least 15-20 minutes. The longer it cools, the thicker the syrup sauce will thicken. Serve with homemade whipped cream or vanilla ice cream.
9. Homemade whipped cream (to make 1 cup): Put 1/2 cup heavy cream into a bowl with 2-4 teaspoons of maple syrup (depending on sweetness preference – I do 3 teaspoons) and whisk on high with a milk frother or electric mixer until thickened. I personally used a milk frother and it takes a few minutes total for a super thick whipped cream.

Notes:

• If you like a lot of streusel topping, then increase the streusel recipe slightly.
• You can use regular flour instead of oat flour if desired. I do not advise using almond flour or coconut flour.
• Make the recipe dairy-free by using coconut oil instead of butter – but just be aware there may be a slight hint of coconut flavor unless you use refined coconut oil (if you use refined, please make sure to buy naturally refined). 
• Substitute another nut in place of the pecans if needed. Almonds, walnuts, or macadamia nuts would work well.
• Omit the pecans if you are nut-free.