Preheat the oven to 350 degrees. Line 24 standard muffin tins with paper liners. Whisk together cake flour, cocoa and salt. With an electric mixer on medium-high speed, whisk together sugar and oil until combined.
Add eggs, beating until each is incorporated. Mix in food color and vanilla. Reduce speed to low. Add flour mixture in 3 batches, alternating with 2 additions of buttermilk, and whisking well after each. Stir together the baking soda and vinegar in a small bowl (it will foam); add mixture to the batter, and mix on medium speed for 10 seconds.
Divide batter evenly among lined cups, filling each three-quarters full. Bake, rotating tins halfway through, until a cake tester inserted in centers comes out clean, about 20 minutes. Transfer tins to wire racks to cool completely before removing cupcakes. Cupcakes can be stored overnight at room temperature or frozen for up to 2 months, in an airtight container. Refrigerate for up to 3 days in airtight containers. Bring to room temperature before serving. Makes 24 cupcakes.
Cream Cheese Frosting: Makes 4 cups.
1 cup (2 sticks) unsalted butter, room temperature
12 ounces cream cheese, room temperature
1 pound (4 cups) confectioners' sugar
3/4 teaspoon vanilla extract
Beat butter and cream cheese on medium until fluffy, about 3 minutes. Reduce to low and add sugar, 1/2 cup at a time, then vanilla. Mix until smooth. If not using immediately, frosting can be refrigerated up to 3 days in an airtight container. Before using, bring to room temperature and beat on low speed until smooth again.