Preheat your oven to 325° F. Line an 8-inch square baking pan with nonstick aluminum foil (or spray with nonstick cooking spray).
In a small saucepan, place the butter and sugar, and melt 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.
In a large bowl of a stand mixer with paddle attachment, place the eggs and vanilla, and mix on low until well-beaten and combined. Add the melted and cooled butter and sugar to the bowl slowly, stirring constantly.
Add the cocoa powder and mix until fully combined. Beat for a minute or two on medium speed.
Add the flour, xanthan gum, cornstarch, baking soda, and salt, and mix on slow until just combined. Add about 4 ounces of the chocolate chips and mix by hand until distributed
Transfer the batter to the prepared pan and spread into an even layer. Scatter the remaining chocolate chips evenly over the top of the brownie batter and press in gently with a silicone spatula.
Place in the center of the preheated oven and bake just until the brownies are no longer wet in the center, about 25-28 minutes. Cool in pan until lukewarm. Place in refrigerator until chilled, to allow for easier cutting. Cut into bite-sized squares