1. Preheat oven to 325°F (163°C). Grease and line a 9-inch springform pan. Whisk flour, baking soda, salt, and cocoa powder. In another bowl, beat oil and sugar. Add egg, then mix in buttermilk, red food coloring, vanilla, and vinegar. Combine wet and dry ingredients until smooth. Pour into the pan and smooth the top.
2. Beat softened cream cheese until fluffy. Add sugar and beat until smooth. Mix in eggs one at a time, then add vanilla. Pour gently over red velvet batter and smooth the top.
3. Bake for 55–65 minutes, until the center is just set. Turn off oven, crack the door, and let cheesecake cool inside for 30 minutes. Then cool completely on a rack and refrigerate for at least 6 hours or overnight.
Notes
Let the cheesecake cool completely to avoid cracks and ensure a clean slice.