Preheat oven to 350F (180C). Butter the sides and bottom of a 8 inch (20cm) springform pan and line the bottom with parchment paper.
Melt the chocolate and butter in a medium bowl, over bain-marie, stirring occasionally, until smooth. Remove the pan from heat but keep the bowl over the water. Stir in the sugar, then remove the bowl from the pan. Cool slightly.
Incorporate the eggs one at a time into the mixture and whisk until well combined. Stir in the vanilla extract, salt, cocoa powder, red food coloring gel and vinegar.Then add the flour and stir well.
Reserve about 3 or 4 tablespoons of batter for later and pour the rest in the prepared pan.
Add cream cheese into a medium bowl and stir until smooth. Add sugar, vanilla and egg yolk and mix to combine.
Add spoons of cream cheese mixture on top of brownie batter. Add teaspoons of reserved brownie on top. Use a skewer to create swirls.
Bake for about 28-30 minutes until a toothpick inserted into the center comes out with a few moist crumbs sticking to it.
Remove the brownie from the oven and cool completely.