Preheat your oven to 350°F. Grease a 13 x 9-inch baking dish and set it aside.
Prepare the crisp topping.
In a medium-sized bowl, place the flour, xanthan gum, oats, granulated sugar, cinnamon, optional nutmeg and salt, and mix to combine. Add the brown sugar, and mix again, working out any lumps.
Add the melted butter, and mix to combine well. The mixture will be thick. Chill only briefly if at all loose or warm. Set the topping aside.
Prepare the apple filling.
In a large bowl, place flour, cinnamon, salt, and brown sugar, and toss to combine well, breaking up any lumps in the brown sugar. Add the apples, and toss to coat the apples completely.
Transfer the filling to the prepared baking dish, add the 1/4 cup lukewarm water and vanilla extract, and stir to combine again. Spread the apple chunks into an even layer.
Place the baking dish on a rimmed baking sheet, cover the dish with aluminum foil, and place it in the oven to begin to soften the apples. Bake for 15 minutes, then remove and uncover the dish to stir the apples. Cover again, return to the oven, and continue to bake for another 15 minutes.
Remove the baking dish from the oven and place on a heatproof surface. Remove the foil, stir the apples and spread them again into an even layer.
Scatter the crisp topping evenly on top, breaking up any larger clumps of topping, and press gently on top to help the topping adhere to the apples.
Return the dish to the oven and bake, uncovered, until the topping is golden brown (about 25 minutes). Remove from the oven and allow to cool for 15 minutes before serving warm, topped with the optional vanilla ice cream.
To replace the oats: Try 50 grams of quinoa flakes, or an additional ¼ cup (36 g) of your all purpose gluten free flour blend. Proceed with the rest of the recipe as written. To replace the gum-free gluten free flour blend: Try an equal amount, by weight, tapioca starch/flour.
Gluten Free Apple Crisp from Nicole Hunn at Gluten Free on a Shoestring. Find recipe online at https://glutenfreeonashoestring.com/gluten-free-apple-crisp/