Preparation

• Preheat the oven to 350 degrees F (175 degrees C). Grease an 8x8-inch baking pan.
• Whisk 1 cup sugar and melted butter in a large mixing bowl; stir in cocoa, red food coloring, 1 teaspoon vanilla extract, vinegar, and salt, one at a time, mixing well after each addition to avoid lumps. Mix in 2 eggs until thoroughly combined.
• Stir flour into cocoa mixture just until combined; set aside ¼ cup batter. Pour remaining batter into the prepared baking dish.
• Beat cream cheese in a bowl using an electric mixer on medium speed until light and fluffy. Add ¼ cup sugar, 1 egg, and ¼ teaspoon vanilla extract; continue to beat until well blended.
• Spoon cream cheese mixture in dollops over the batter in pan; gently smooth tops of dollops even with batter using a knife or offset spatula. Drizzle reserved ¼ cup of batter over the dollops of cream cheese mixture. Drag a knife through the batter and cream cheese mixture to create swirls.
• Bake in the preheated oven until top is dry and edges have started to pull away from the sides of the pan, about 30 to 35 minutes. Cool completely before cutting into bars; store covered in refrigerator.