01 - Preheat oven to 350°F. Line 8x8 inch baking pan with parchment paper, leaving overhang for easy removal.
02 - Whisk melted butter and sugar until smooth in large bowl. Add eggs, vanilla extract, and red food coloring; whisk until fully combined.
03 - Sift flour, cocoa powder, and salt into batter. Fold gently with spatula until just combined; avoid overmixing.
04 - Reserve 1/4 cup red velvet batter. Pour remaining batter into prepared pan and spread evenly.
05 - Beat cream cheese with sugar until smooth. Add egg and vanilla extract; mix until creamy.
06 - Pour cheesecake mixture over brownie batter in pan. Smooth evenly with spatula.
07 - Drop spoonfuls of reserved red velvet batter over cheesecake layer. Use knife or skewer to gently swirl batters together for marbled effect.
08 - Bake for 33-36 minutes until center is just set and toothpick inserted comes out with few moist crumbs.
09 - Cool completely in pan on wire rack before lifting out and cutting into squares.