Preheat the oven to 350°F (175°C) and grease 2 one-cup ramekins.
Prepare the topping. In a small mixing bowl, mix the dry ingredients together and then add the melted fat. Set aside.
2 tablespoons (12 grams) oat flour, 3 tablespoons (16 grams) rolled oats, 1/2 teaspoon cinnamon, 17 grams coconut sugar, pinch salt, 1 1/2 tablespoons (21 grams) unsalted butter
Prepare the filling. In a medium mixing bowl, mix together everything except for the apples until well combined. Stir in the apple chunks and stir to coat.
2 tablespoons maple syrup, 1 teaspoon vanilla extract, 1 teaspoon cornstarch, 1/4 teaspoon cinnamon, 1/8 teaspoon nutmeg, pinch salt, 2 cups (220 grams) apple chunks
Divide the filling between the two prepared ramekins. Sprinkle the topping evenly over the top of each one.
Place the crumbles on a baking sheet (just in case there are any spills, which there shouldn't be).
Bake for 22-26 minutes or until the topping is firm and golden brown. The apples should be bubbling.
Serve immediately or cool and cover and refrigerate any leftovers for up to 3 days.