Preheat your oven to 350°F (175°C). Grease and line an 8x8-inch baking pan with parchment paper.In a large mixing bowl, whisk together the melted butter, granulated sugar, and brown sugar until smooth.Add the eggs one at a time, whisking well after each addition. Stir in the vanilla extract.Sift in the cocoa powder, flour, salt, and espresso powder (if using). Mix gently until just combined.Fold in the chocolate chips or chopped chocolate using a rubber spatula.Pour the batter into the prepared baking pan and spread it evenly.Bake for 28–32 minutes, or until the edges are set and a toothpick inserted into the center comes out with a few moist crumbs.Allow the brownies to cool in the pan for 30 minutes before lifting them out and slicing into squares.
