Prep the oven: Preheat to 350°F (175°C) and line two muffin pans with cupcake liners.
Mix dry ingredients: In a medium bowl, whisk together flour, cocoa powder, baking soda, and salt.
Cream butter and sugar: In a large bowl, beat softened butter and sugar until light and fluffy—about 2-3 minutes.
Add eggs: Beat in eggs one at a time, making sure each is fully mixed before adding the next.
Add sour cream, milk, red food color, and vanilla: Mix until fully combined.
Combine wet and dry: Gradually add the dry ingredients to the wet, mixing just until combined. Don’t overmix!
Fill cupcake liners: Spoon batter into liners about 2/3 full.
Bake: Bake for 18-20 minutes, or until a toothpick inserted in the center comes out clean.
Cool: Let cupcakes cool in the pan for 5 minutes, then transfer to a wire rack to cool completely before frosting.