01 - Preheat oven to 325°F. Grease a 9-inch springform pan and line the base with parchment paper.
02 - In a bowl, whisk together flour, cocoa powder, baking soda, and salt until well combined.
03 - In a separate bowl, beat sugar, oil, and egg until light and fluffy. Mix in buttermilk, vinegar, vanilla, and red food coloring until incorporated.
04 - Gradually add dry ingredients to wet mixture, mixing until just combined. Pour batter into prepared pan and spread evenly.
05 - Bake for 15 minutes. Center may appear slightly underdone, as it will finish baking with cheesecake layer.
06 - Beat cream cheese and sugar until smooth and creamy. Add eggs one at a time, beating well after each addition. Mix in sour cream, vanilla, and flour until just combined.
07 - Pour cheesecake batter over partially baked red velvet layer. Smooth top and bake for 1 hour 5 minutes until center is just set with slight wobble.
08 - Turn off oven, crack door open, and let cheesecake cool inside for 1 hour to prevent cracking.
09 - Remove from oven and cool to room temperature. Refrigerate for at least 6 hours or overnight until completely set.
10 - Beat cream cheese and butter until fluffy. Add powdered sugar and vanilla, beating until smooth and spreadable.
11 - Release cheesecake from springform pan. Frost if desired, slice into portions, and serve chilled.