Preheat your oven to 350°F (175°C) and grease a 9x9 inch baking pan.

In a large mixing bowl, whisk together the melted butter and granulated sugar until glossy. Add eggs one by one and then vanilla extract.

Gently fold in flour, cocoa powder, and salt until just combined.

In a separate bowl, beat cream cheese until smooth. Gradually add sugar, egg, and vanilla, mixing until combined. Add red food coloring if using.

Pour half of the brownie batter into the pan. Top with cheesecake mixture, then spoon remaining brownie batter over it.

Gently swirl the layers with a knife or skewer to create a pattern.

Bake for 30-35 minutes until edges pull away. A toothpick should come out with moist crumbs.

Cool in the pan for 1-2 hours before lifting out and slicing into squares.