Preheat oven to 325°F. Line a 9x9-inch metal baking pan with parchment paper and spray with gluten-free nonstick cooking spray.
In a large bowl, whisk together the sugar, cocoa powder, flour, xanthan gum, baking soda, salt, and cornstarch.
In a separate bowl, beat the eggs and then beat in the melted butter, oil, vanilla extract, and bourbon. Mix the wet ingredients into the dry ingredients until the dry ingredients are fully incorporated. Fold in the chocolate chips.
Transfer the batter to the prepared pan and bake for 22-25 minutes. Cool completely in the pan before cutting.
Chill the brownies for 30 minutes for cleaner cut slices.
This recipe can be doubled and baked in a 9x13 pan.
Store leftover brownies at room temperature in an airtight container up to 2 days or in the refrigerator up to 1 week. These brownies also freeze well.