Preheat the oven to 350°F. Grease a 9x9" baking pan with cooking spray and line with parchment paper.
In a large bowl, whisk together brown butter, eggs, and vanilla extract until smooth.
1 cup brown butter, 3 large eggs, 2 tsp pure vanilla extract
Add in sugars and mix well.
3/4 cup granulated sugar, 1 cup brown sugar
Sift cocoa powder, flour, espresso powder, and salt into the bowl and fold with rubber spatula until just combined.
3/4 cup cocoa powder, 1 cup all-purpose flour, ½ tsp espresso powder, ½ teaspoon salt
Fold in chocolate chips, chocolate chunks, and pecans.
2/3 cup semi-sweet chocolate chips, 1 king size Hershey's milk chocolate bar, 1 cup chopped pecans
Add batter to pan and smooth to the edges
Bake for 30-35 minutes or until center is set. OR, if you like your brownies extra gooey, check them at 25 minutes and remove from the oven when the center is just barely set.
Cool in pan for 20 minutes and then transfer to a wire rack to cool completely.
Dust with powdered sugar before serving, if desired.
*Brown butter: You can see step-by-step details on how to brown butter in my Brown Butter Appreciation Post. But if you prefer a quicker recipe, you can just melt the butter in your microwave and these will still be fantastic brownies!**Toasting pecans: I used a couple packets of chopped pecans from the baking aisle, and toasted them in a pan for about 5-10 minutes on medium heat, until fragrant.