Preheat oven to 350 degrees Fahrenheit. Line cupcake pan with 24 cupcake liners.
In a large mixing bowl, cream together butter and sugar. Add eggs and vanilla, mix well. Add in flour, baking powder, and salt, mix well. Stir in milk and sour cream.
Fill cupcake liners ⅔ full, about 3 tablespoons each.
Bake in the oven for 15-18 minutes until a toothpick inserted into the center of the cupcakes comes out clean.
Chocolate Buttercream Frosting
In a large mixing bowl, add butter, shortening, vanilla, and cocoa powder. Mix well. Slowly alternate adding in confectioners' sugar and evaporated milk, blending well after each addition.
Frost cupcakes once they have fully cooled.