Preheat your oven to 350°F (175°C). Line an 8x8 inch baking pan with parchment paper.
In a large bowl, whisk together melted butter and 1 cup sugar. Stir in eggs, red food coloring, and 2 tsp vanilla.
Sift in the cocoa powder, salt, and flour. Stir until just combined.
Pour the batter into the prepared pan and smooth the top.
In a separate bowl, mix cream cheese, 1/4 cup sugar, egg yolk, and 1/2 tsp vanilla until smooth.
Drop spoonfuls of the cream cheese mixture on top of the brownie batter. Swirl gently with a knife.
Bake for 25–30 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.
Cool completely before slicing. If you can wait that long!