01 - Preheat oven to 350°F. Line an 8-inch square baking pan with parchment paper.
02 - In a large bowl, whisk together melted butter, granulated sugar, and light brown sugar until glossy and combined.
03 - Beat in eggs and vanilla extract until the mixture is smooth and slightly thickened.
04 - Sift together flour, cocoa powder, and salt; gently fold into the wet mixture until just combined without overmixing.
05 - Stir in chopped dark chocolate evenly.
06 - Pour batter into prepared pan and smooth the surface.
07 - Bake for 22 to 25 minutes until edges are set but center remains slightly fudgy. Avoid overbaking.
08 - Allow to cool in the pan for 10 minutes, then cut into squares while warm.
09 - Serve warm with a scoop of vanilla ice cream; optionally add chocolate sauce, nuts, or berries.