2 cups all purpose gluten free flour
1 teaspoon xanthan gum (omit if your blend already contains it)
1/4 cup cornstarch
3/4 teaspoon kosher salt
1 teaspoon baking powder
1/2 teaspoon baking soda
2 teaspoons pumpkin pie spice*
2/3 cup sugar
2 tablespoons packed light brown sugar
6 tablespoons unsalted butter, at room temperature
2 eggs at room temperature, beaten
2/3 cup buttermilk, at room temperature
5 ounces pumpkin butter, homemade or store bought, at room temperature
*To make your own pumpkin pie spice, combine 1 teaspoon ground cinnamon + 1/2 teaspoon ground ginger + 1/4 teaspoon ground allspice, 1/4 teaspoon ground cloves + 1/8 teaspoon ground nutmeg.
Preheat your oven to 350°F. Grease a standard 9-inch x 5-inch loaf pan and set it aside.
In a large bowl, place the flour, xanthan gum, cornstarch, salt, baking powder, baking soda, pumpkin pie spice and sugars, and whisk to combine well, breaking up any lumps in the brown sugar. Create a well in the center of the dry ingredients, and add the butter, eggs, buttermilk and pumpkin butter, mixing to combine after each addition. The batter will be very thick.
Scrape the batter into the prepared pan, pressing it into all corners of the pan. With wet fingers and/or a wet spatula, smooth the top of the batter into an even layer.
Place the loaf pan in the center of the preheated oven and bake until the top is domed and lightly golden brown in color, and a toothpick inserted in the center comes out with no more than a few moist crumbs attached (nothing gooey at all!) (45 to 55 minutes). Remove the pan from the oven and allow to cool for 10 minutes before turning out onto a wire rack to cool completely. Slice and serve once cool.