01 - Preheat oven to 350°F. Line a 24-cup mini muffin tin with paper liners or lightly grease with nonstick spray.
02 - In a medium bowl, whisk together melted butter and sugar until combined. Add eggs, vanilla extract, and red food coloring; mix well.
03 - Sift in the flour, cocoa powder, and salt. Stir until just combined; do not overmix.
04 - Divide the red velvet brownie batter evenly among the mini muffin cups, filling each about 2/3 full.
05 - In a separate bowl, beat the cream cheese until smooth. Add sugar, egg yolk, and vanilla extract; mix until creamy and fully blended.
06 - Add a small spoonful of cheesecake mixture on top of each brownie cup. Use a toothpick or skewer to gently swirl the cheesecake into the brownie batter for a marbled effect.
07 - Bake for 22-25 minutes, or until the centers are set and a toothpick inserted comes out mostly clean with a few moist crumbs.
08 - Cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before serving.