Heat oven to 375℉ and butter an 8×8-inch square pan.
In a large bowl, combine the 1 ¼ cup gluten-free oats, 1 cup almond flour, ¾ cup dark brown sugar, ½ teaspoon ground cinnamon and ½ teaspoon ground ginger, and ¼ teaspoon fine sea salt. Whisk and stir together to combine. Rub in the 10 tablespoons unsalted butter with your hands, working it in until the mixture resembles a very coarse meal.
Spread half the butter and oat mixture evenly in the bottom of the pan, pressing it in lightly. Cover with the chopped 6 apples. Sprinkle the remaining crisp mixture on top of the apples and spread it to cover the fruit as evenly as possible.
Place in the oven and bake for about 40-50 minutes, until fruit is bubbling a bit and the topping is crisp. Remove from oven and let cool to room temperature. Serve with vanilla ice cream.
Notes
Let it rest: In the recipe instructions, I advise letting the crisp cool to room temperature after baking to allow the crisp filling to solidify a bit. You can gently rewarm it in the oven before serving or just serve it at room temperature.
Add nuts - Instead of the 1 cup of rolled oats, substitute 1 cup of sliced almonds (you can toast them lightly or leave them untoasted). Or, add ½ cup of chopped walnuts to the topping and leave in the oats.
Oats and almond flour substitute - Use 2 ½ cups of your favorite 1:1 gluten free flour blend instead of the oats and almond flour.
Make it dairy-free - Substitute your favorite non-dairy butter for the butter to make this oatmeal apple crisp dairy-free.
Adjust the sugar - Depending on your apples, you can add more or less sugar to taste. For example, you may want to add more sugar if you use Granny Smith apples because they are more tart.