Preheat your oven to 350°F and spread the pecans on a baking sheet. Toast for 8-10 minutes, stirring halfway through, until fragrant and lightly browned. Remove from the oven and let cool completely on the sheet—this takes about 5 minutes. Once cooled, chop the pecans into roughly 1/4-inch pieces and set aside. While the pecans cool, line your 9x13 inch baking pan (or 8x8 inch for thicker brownies) with parchment paper, leaving some overhang on the sides for easy removal later.
Cut the butter into a few pieces and place in a small saucepan over medium heat. Let it melt and continue cooking for 6-8 minutes, swirling the pan occasionally, until the milk solids turn a deep amber color and smell nutty—this is where the magic happens for flavor. Pour the browned butter into a bowl and set aside to cool slightly. While the butter cools, finely chop the dark chocolate into 1/2-inch chunks and place in a microwave-safe bowl. Microwave in 20-second intervals, stirring between each interval, until completely melted and smooth. Let the chocolate cool for a few minutes while you proceed.
Reduce your oven temperature to 320°F now so it's ready when you need it. In a large mixing bowl, combine the room-temperature eggs and brown sugar. Using an electric mixer on medium-high speed, whip for 5-7 minutes until the mixture is pale, fluffy, and has roughly tripled in volume—this incorporates air that gives brownies their tender crumb. I find room-temperature eggs whip more efficiently and create more volume, which is important for gluten-free baking where we need all the structure we can get.
Pour the cooled browned butter into the whipped egg mixture and fold gently with a spatula until no streaks of butter remain. Then add the cooled melted chocolate and fold until fully incorporated and the batter is uniformly dark. Don't overmix at this stage—you want to maintain the airiness you just created.
In a separate small bowl, sift together the gluten-free flour, cocoa powder, xanthan gum, salt, and vanilla extract. Sifting the cocoa powder removes any lumps and ensures even distribution of the xanthan gum, which helps bind the batter in place of gluten. Add this dry mixture to the wet ingredients from Step 4 and fold gently with a spatula until just combined—stop folding as soon as you don't see any streaks of flour. Overmixing develops gluten-free flour differently and can make brownies tough instead of fudgy.
Fold most of the toasted pecans (reserve about 2 tablespoons for topping) into the batter until evenly distributed. Pour the batter into your prepared pan and spread into an even layer. Sprinkle the reserved pecans across the top, pressing them gently into the surface so they stay in place during baking.
Bake at 320°F for 20-22 minutes if you prefer gooey, fudgy brownies with a slight jiggle in the center, or 24-26 minutes for denser, fully set brownies. The center should still look slightly underbaked when you remove the pan—brownies continue cooking slightly from residual heat as they cool. Let them cool completely in the pan at room temperature (this takes about 1-2 hours), then use the parchment paper overhang to lift them out and transfer to a cutting board. Cut into squares with a sharp knife, wiping the blade between cuts for clean edges.
