Preheat oven to 350°F (175°C). Line mini cupcake pans with liners.
Whisk flour, cocoa, baking soda, and salt in a bowl.
Combine oil, egg, buttermilk, food coloring, vanilla, and vinegar in another bowl.
Fold dry ingredients into wet until just combined. Do not overmix.
Fill cupcake liners ¾ full. Bake 12–15 minutes. Cool completely.
Beat cream cheese and butter until fluffy. Add powdered sugar, vanilla, salt.
Frost cooled cupcakes using piping bag or spatula.
Optional: Rest batter 5 minutes before baking for best texture.