Preheat your oven to 350°F (175°C). This step is crucial to ensure even baking.
Line your 9x13 inch baking pan with parchment paper, leaving some overhang on the sides. Lightly grease the parchment paper.
In a medium saucepan, melt the butter over low heat. Remove from heat once melted and allow to cool slightly.
Add the brown sugar and granulated sugar to the melted butter. Whisk until well combined and smooth.
Add the eggs, one at a time, whisking well after each addition. Then mix in the vanilla extract until fully incorporated.
In a separate bowl, whisk together the cocoa powder, flour, espresso powder, and kosher salt.
Gradually fold the dry ingredients into the wet ingredients using a rubber spatula. Combine just until you see no dry flour.
If you're using chocolate chips and/or pecans, gently fold them into the brownie batter.
Spread the brownie batter evenly into your prepared baking pan.
Bake in the preheated oven for 20-25 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.
Let the brownies cool in the pan for about 10 minutes before lifting them out using the parchment paper. Allow them to cool completely on a wire rack before slicing into squares.
