Preheat and prepare pan. Preheat oven to 350°F (177°C). Grease and flour an 8-inch square pan or line with parchment paper.
Melt the butter. In a light-colored skillet (it's easier to see the butter browning in a lighter colored skillet) on medium-low heat, melt the butter. I find it easier and faster to cut the butter into tablespoons first. Be sure to stir your butter as it melts, to ensure it melts evenly. 12 tablespoons (1 ½ sticks, 170 g) unsalted butter
Continue to stir the butter. Once the butter is melted, it will begin to foam and bubble. It will also look cloudy in appearance to start and then become clear as it continues to cook. During this step, the butter can splatter due to all that water evaporating. Stir the butter mixture and let it cook. You want to be stirring the butter and keep a close eye on the butter so it doesn't burn.
Brown the butter. The butter will begin to foam about 5 minutes and milk solids will begin to form at the bottom of the process. As the milk solids become golden brown, you will see the butter start to turn a golden brown color as well. The butter will begin to turn brown, but sometimes the foam makes that hard to see. So clear the foam way and check the color. If it's a golden brown, caramel color it's ready. You want the butter to be hot for the next step.
Combine browned butter and dry ingredients (except flour) . In a large mixing bowl, stir together with a spatula or wooden spoon the (still hot) browned butter, sugar, brown sugar, cocoa powder, espresso powder and salt. Let Cool slightly before adding eggs in next step. 1 cup (200 g) granulated white sugar ¾ cup (90 g) packed light brown sugar ¾ cup (63 g) cocoa powder ½ teaspoon instant espresso powder ½ teaspoon salt
Add wet ingredients. whisk in the eggs, and vanilla until smooth. 3 large eggs 2 teaspoons vanilla extract
Add flour and chocolate chips. Stir in with a spatula the flour, just until combined. Be sure to not overmix at this point. The more you mix the cakier your brownies will be. Fold in the chocolate chips. Spread batter into prepared pan. ¾ cup (90 g) all-purpose flour 1/2 cup (85 g) semi-sweet chocolate chips
Bake. Bake in preheated oven for 25-30 minutes until the edges look dry but the middle is slightly soft, and underdone. Remove from the oven and allow to cool. Cut into bars and serve.