Preheat & Prep. To start, preheat the oven temperature to 350 degrees F. Line a metal 8x8 baking pan with parchment paper, and set aside.
Melt. In a medium microwave-safe bowl, combine 1/2 cup chocolate chips, the butter, and the oil. Melt in 20-30 second intervals, stirring in between each interval until chocolate is smooth and glossy.
Whip Sugar & Eggs. In a large bowl (ideally glass), combine sugar, brown sugar, and eggs. Use an electric hand mixer to beat the eggs 5-6 minutes on medium speed, or until doubled in volume and very light in color. When you lift the beaters out of the mixture, you should be able to see the batter drizzle down in a smooth stream and land on the surface before dissolving. Do NOT rush this step, or the sugar won't dissolve properly and the brownies won't have the glossy top crust we're going for. Do the full 5-6 minutes! Add Chocolate Mixture to Egg Mixture and use a spatula to stir until combined. Mix In Vanilla and stir to combine.
Sift In Dry Ingredients. Use a fine mesh sieve or sifter to sift in cocoa powder, gluten-free flour, and salt. Stir until almost fully combined with just a few dry patches left.
Fold In The Chocolate Chips. Then, use your spatula to gently fold in 2/3 cup chocolate chips and mix until *just* combined, with the chocolate chips evenly distributed and no floury patches remaining.
Pour Batter Into The Prepared Pan and use an offset spatula to smooth the surface of the brownies into an even layer.
Bake Brownies in preheated oven for 30-35 minutes, or until the top is glossy and set and a toothpick inserted in the center comes out with some moist crumbs (but not glossy wet batter).