Gluten Free Caramel Apple Shortbread Squares
1 3/4 cups (245 g) all-purpose gluten-free flour
1/2 teaspoon xanthan gum (omit if your blend already contains it)
1/8 teaspoon kosher salt
1/2 cup (100 g) sugar
8 tablespoons unsalted butter, at room temperature
1 to 2 tablespoons lukewarm water
3 to 4 baking apples (I used a mixture of Macintosh and Granny Smith), peeled, cored and sliced very thin
2 tablespoons (25 g) sugar
1 teaspoon ground cinnamon
1/8 teaspoon kosher salt
Simple syrup, for brushing*
2 cups (400 g) granulated sugar
1/2 cup (4 fluid ounces) water, at room temperature
1/4 teaspoon cream of tartar
3/4 cup (6 fluid ounces) heavy whipping cream, at room temperature
6 tablespoons (84 g) unsalted butter, at room temperature
1 teaspoon pure vanilla extract
Coarse salt, for sprinkling (optional)
*To make your own simple syrup, combine equal parts sugar and water, and heat gently in a small, heavy-bottom saucepan until the sugar is completely dissolved. Do not boil the sugar. My favorite sugar for making simple syrup is Sugar in the Raw, as it dissolves completely in water.
**Instead of making your own caramel, you can melt packaged soft caramels to pour over the apple shortbread.
Preheat your oven to 325°F. Line a quarter sheet pan (9-inch x 13 inch rimmed baking sheet) with unbleached parchment paper and set it aside.
First, make the shortbread layer. In a large bowl, place the flour, xanthan gum, salt and sugar, and whisk to combine well. Add the butter and 1 tablespoon water, and mix to combine. The dough will be a bit dry, and you will have to knead it with your hands to get it to come together. If necessary for the dough to hold together, add a second tablespoon of water, 1 teaspoon at a time. Transfer the dough to the prepared baking sheet, and press into an even layer. Cover with another sheet of unbleached parchment paper and smooth out the dough by pressing it down evenly. Set the pan aside.
Prepare the apple layer. In a large bowl, place the sliced apples, sugar, cinnamon and salt, and toss to coat the apples evenly. Lay the apple slices, overlapping one slightly on the other, in three rows along the length of the shortbread in the quarter sheet pan. Brush the apples lightly with the simple syrup. Place the pan in the center of the preheated oven and bake until the apples are tender and the shortbread is just beginning to brown around the edges (about 15 minutes). Remove from the oven and allow to cool.
Make the caramel layer. Place the sugar, water and cream of tartar in a medium-size, heavy-bottom saucepan and whisk to combine. Cook, undisturbed, over medium-high heat until the sugar begins to turn amber-colored around the edges and reaches 305°F. Remove the saucepan from the heat, stir to prevent the sugar from burning, and add the heavy cream. The mixture will bubble up quite a lot. Stir until the bubbling subsides. The sugar may seize up, but it will melt again. Add the butter, and stir to combine. Return the saucepan to the heat and cook undisturbed, over medium-high heat, until the mixture reaches 245°F. Remove from the heat and whisk in the vanilla. Immediately pour the caramel in an even layer over the top of the baked apples and shortbread in the baking sheet. Sprinkle lightly with the (optional) finishing salt. Allow to sit at room temperature until set before slicing into squares and serving.