Heat oven to 350°F. Line a 12-cup muffin pan with paper liners.
Whisk flour, sugar, cocoa, baking soda, and salt in a large bowl.
Whisk buttermilk, oil, eggs, vanilla, and vinegar in a separate bowl until smooth.
Stir in red food coloring to reach a deep ruby shade.
Pour wet mixture into dry. Fold just until combined; small lumps are fine.
Scoop batter into liners, filling each about two-thirds full.
Bake 17 to 20 minutes, until a toothpick comes out clean.
Cool in pan 5 minutes. Transfer cupcakes to a rack to cool completely.
Beat cream cheese and butter on medium until fluffy, about 2 minutes.
Gradually add powdered sugar, salt, and vanilla. Beat until smooth and creamy.
Mix in heavy cream a little at a time for spreadable consistency.
Swirl frosting onto cooled cupcakes. Add sprinkles or crumbs if you like.