Bring cream cheese, eggs, and butter to room temperature before mixing to ensure smooth, lump-free batter and better incorporation of the cheesecake swirl.

The white vinegar reacts with the baking soda to activate the red food coloring, so don't skip it—mix it in gently to avoid deflating your batter.

Pour half the chocolate batter first, add dollops of cream cheese mixture, then top with remaining chocolate and swirl with a knife before baking for optimal marbling without over-mixing.

Use unsweetened cocoa powder and don't substitute it with Dutch-process; the natural acidity helps develop the classic red velvet flavor and works with the vinegar.

Insert a toothpick in the center—it should have a few moist crumbs, not be completely clean, ensuring fudgy brownies that won't overbake during cooling.