9 tablespoons (126 g) unsalted butter, chopped
1 1/4 cups (250 g) granulated sugar
2 eggs (100 g, weighed out of shell), at room temperature
1 teaspoon pure vanilla extract
1 cup (80 g) unsweetened cocoa powder (natural or Dutch-processed)
1/3 cup (47 g) all purpose gluten free flour (I used Better Batter)
1/8 teaspoon xanthan gum (omit if your blend already contains it)
2 tablespoons (18 g) cornstarch
1/8 teaspoon baking soda
1/4 teaspoon kosher salt
5 ounces semi-sweet chocolate chips
Preheat your oven to 325°F. Line an 8-inch square baking pan with nonstick aluminum foil (or line with regular aluminum foil and spray with nonstick cooking spray). Set the pan aside. In a small saucepan, place the butter and sugar, and place over medium heat, whisking occasionally, until melted and simmering. Remove the saucepan from the heat and set it aside to cool until no longer hot to the touch. Alternatively, place the bottom of the saucepan in a bowl of cool water to speed the cooling process, but make sure the butter does not solidify.
In a large bowl, place the eggs and vanilla, and whisk until well-beaten and combined. Add the melted and cooled butter and sugar to the bowl slowly, whisking constantly. Add the cocoa powder and whisk until the cocoa powder has been absorbed. Using a handheld mixer, beat until very well-combined. Add the flour, xanthan gum, cornstarch, baking soda, and salt, and mix with a silicone spatula or spoon until just combined. Add about 4 ounces of the chocolate chips and mix until just evenly distributed throughout the batter. The batter will be thick and sticky.
Transfer the brownie batter to the prepared pan and, using an offset or silicone spatula, spread into an even layer. It helps to moisten the tool you are using to smooth the top a bit to prevent it from sticking. Scatter the remaining chocolate chips evenly over the top of the brownie batter and bang the pan firmly on the countertop to help the chips adhere. Place in the center of the preheated oven and bake just until the brownies are no longer wet in the center, about 28 minutes. The center may dome during baking, but the brownies will settle as they cool.
Remove the brownies from the oven and allow them to cool in the pan at room temperature until the pan is no longer hot to the touch. For clean lines when you slice the brownies, place the brownies, still in the pan, in the refrigerator to chill for about an hour before removing them from the pan, peeling away the foil, slicing, and serving. These freeze incredibly well.