Homemade Hostess Cupcakes

Preheat the oven to 375 degrees F (180 degrees C). Line 36 muffin cups with paper cups.

Whisk together flour, white sugar, cocoa, baking soda, and salt in a large bowl. Add eggs, milk, oil, water, and vanilla extract. Mix with an electric mixer at low speed until smooth, about 2 minutes. Fill prepared muffin cups a little over half full (use a #20 or 3-tablespoon scoop).

Bake until a toothpick inserted in centers comes out clean, 18 to 22 minutes. Transfer from pans to wire racks to cool completely.

Meanwhile, for the filling, combine powdered sugar, butter, shortening, milk, vanilla extract, and a pinch salt in another large bowl. Using clean beaters, mix with an electric mixer at high speed until fluffy, about 5 minutes. Insert a large round tip into a pastry bag; fill with filling. Push tip through top of each cooled cupcake to fill; wipe excess frosting off to create a smooth top.

Frost tops with chocolate frosting. Insert a small round tip into a clean pastry bag; fill with vanilla frosting. Pipe frosting across tops of cupcakes in loops. Transfer cupcakes to an airtight container. Store at room temperature up to 3 days or freeze up to 3 months.