Preheat oven to 350°F. Grease mini bundt pans.
Whisk flour, sugar, baking soda, cocoa, and salt in a bowl.
Whisk buttermilk, oil, eggs, food coloring, vanilla, and vinegar in another bowl.
Fold wet into dry until just mixed. Don’t overmix.
Spoon batter into pans two-thirds full.
Bake 12–15 minutes or until a toothpick comes out clean.
Cool 10 minutes, then unmold onto a rack to finish cooling.
Whisk 4 oz cream cheese, 1 cup powdered sugar, 2 tbsp milk, and 1/2 tsp vanilla until smooth. Drizzle over cakes.