Assemble your ingredients. Line a baking sheet with parchment paper. Preheat the oven to 325℉ (163℃).
In a medium mixing bowl, whisk together the flours, xanthan gum, baking powder, and salt.
1 cup almond flour, 1 cup white rice flour, 1 teaspoon xanthan gum, 1 teaspoon baking powder, ½ teaspoon fine sea salt
In a large mixing bowl, cream the butter (either by hand with a spoon or with an electric mixer). Beat in the sugar until it is smoothly creamed with the butter. Then beat in the eggs and vanilla. You might need to pause and scrape down the sides with a spatula to make sure everything is incorporated.
¼ cup butter, ½ cup raw sugar, 3 large eggs, 1 teaspoon pure vanilla extract
Stir in the lemon zest and dried blueberries.
1 tablespoon lemon zest, ¾ cup dried blueberries
Press the dough out into a long, flatish shape, about 4 inches wide on the parchment-lined baking sheet.
Bake for 30 minutes.
Remove from the oven to cool for about 10 minutes. Cut the oblong shape crosswise into slices about ½ inch thick. Arrange them back onto the parchment paper, on their sides, and bake for another 20 minutes.