1 1/2 cups (210 g) all purpose gluten free flour (I used Better Batter)
3/4 teaspoon xanthan gum (omit if your blend already contains it)
1/2 cup (50 g) certified gluten free old-fashioned rolled oats
1/2 cup (109 g) packed light brown sugar
1/3 cup (67 g) granulated sugar
1 tablespoon ground cinnamon
1/2 teaspoon freshly grated nutmeg
1/4 teaspoon kosher salt
12 tablespoons (168 g) unsalted butter, melted and cooled
3 pounds (about 6 large apples) Granny Smith apples (or other tart and firm apple), peeled, cored and sliced into 1/4-inch thick wedges
2 tablespoons (18 g) gum free gluten free flour blend (or use an equal amount tapioca starch/flour)
1 teaspoon ground cinnamon
1/3 cup (73 g) packed light brown sugar
1/3 cup (40 g) raw pecans and/or almonds, roughly chopped
Vanilla ice cream, for serving (optional)
Preheat your oven to 350°F. Grease a 13 x 9-inch baking dish and set it aside.
First, prepare the crumble topping. In a medium-sized bowl, place the flour, xanthan gum, oats, brown sugar, granulated sugar, cinnamon, nutmeg and salt, and whisk to combine, working out any lumps in the brown sugar. Add the butter, and mix to combine well. The mixture will be thick. Place the bowl in the refrigerator to chill for about 10 minutes or until firm (or the freezer for about 5 minutes).
To make the filling, in a large bowl, place the apples flour, brown sugar and cinnamon, and toss to combine well. Transfer the apple mixture to the prepared baking dish, and spread them into an even layer. Scatter the nuts evenly over the top of the apple filling. Remove the crumble topping from the refrigerator and break it up into large chunks with a fork. Scatter the topping in an even layer all over the top of the apple filling. Press gently on the crumble topping to ensure that it adheres to the filling.
Cover the baking dish with aluminum foil and place it in the center of the preheated oven. Bake for 25 minutes, remove the foil, and continue to bake until the crumble topping is golden brown and the apples are fork tender (about another 20 minutes). Remove from the oven and serve warm by scooping into bowls and topping with the optional vanilla ice cream.