Preheat your oven to 350°F (175°C).
Line a 9x13 inch baking pan with parchment paper.
Melt 1 cup of butter in a medium saucepan over low heat.
In a large mixing bowl, combine melted butter, cocoa powder, brown sugar, and granulated sugar. Whisk until smooth.
Add eggs one at a time, whisking thoroughly after each addition.
In a separate bowl, whisk together flour, espresso powder, and kosher salt. Gradually fold into the wet mixture.
Stir in vanilla extract and fold in chocolate chips and/or pecans if using.
Pour batter into the prepared pan and bake for 25-30 minutes.
Cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.
