For the cookies
2 cups (280 g) all purpose gluten free flour (I used Better Batter)
1 teaspoon xanthan gum (omit if your blend already contains it)
1/4 teaspoon kosher salt
1 1/2 teaspoons baking powder
1 1/2 teaspoons cream of tartar
1 1/2 teaspoons apple pie spice (See Recipe Notes)
3/4 cup (150 g) granulated sugar
3/8 cup (82 g) packed light brown sugar
9 tablespoons (126 g) unsalted butter, melted and cooled
5 ounces apple butter (homemade or store-bought), at room temperature
3 eggs (150 g, weighed out of shell) at room temperature, beaten
For the topping
1/4 cup (50 g) granulated sugar
2 teaspoons ground cinnamon
For the apple pie spice
To make your own apple pie spice, combine 4 teaspoons ground cinnamon + 1/2 teaspoon ground cardamom + 1/2 teaspoon freshly grated nutmeg + 1/4 teaspoon ground ginger + 1/8 teaspoon ground allspice.
Preheat your oven to 350°F. Grease and line a 9-inch square baking pan and set it aside.
In a large bowl, place the flour, xanthan gum, salt, baking powder, cream of tartar, apple pie spice, and granulated sugar, and whisk to combine well. Add the brown sugar and mix, breaking up any lumps. Create a well in the center of the dry ingredients, and add the melted butter, apple butter, and eggs, and mix until combined. The dough will be thick, but soft.
In a small bowl, place the granulated sugar and cinnamon for the topping, and mix to combine. Sprinkle the cinnamon-sugar in a thin layer in the prepared pan. Place the cookie dough in mounds, scattered evenly over the interior surface of the pan, on top of the cinnamon-sugar. Using a moistened spatula, press the cookie dough into a single layer, and smooth the top. Sprinkle the cinnamon-sugar again on top of the cookie dough, in a thin, single layer.
Place the pan in the center of the preheated oven and bake for about 25 minutes or until just firm to the touch all the way to the center. Remove the pan from the oven, place it on a wire rack, and allow it to cool completely before slicing into squares and serving.