01 - Preheat oven to 350°F. Line a 9x9 inch baking pan with parchment paper, leaving an overhang for easy removal.
02 - In a medium saucepan over low heat, melt unsalted butter and chopped dark chocolate together, stirring until smooth. Remove from heat and let cool slightly.
03 - Whisk granulated sugar into the melted mixture. Add eggs and vanilla extract, then whisk until glossy and well combined.
04 - Fold in all-purpose flour and salt until just combined. Avoid overmixing to ensure a tender texture.
05 - In a separate bowl, whisk together ricotta cheese, egg yolk, granulated sugar, and vanilla extract until smooth.
06 - Spread about three-quarters of the brownie batter evenly into the prepared baking pan.
07 - Dollop spoonfuls of ricotta mixture and remaining brownie batter over the surface. Use a knife or skewer to gently swirl the mixtures together for a marbled appearance.
08 - Bake for 35 to 38 minutes, or until the center is set but still moist. A toothpick inserted should come out with a few moist crumbs.
09 - Allow to cool completely in the pan. Lift out using the parchment overhang and slice into squares.