Preheat oven to 350°F. Prepare (2) 12-cup muffin tins with cupcake liners.
Follow the instructions on the box to blend the cake mix, sparkling wine (or water), egg whites and vegetable oil.
Pour the batter into the cupcake liners, about 3 level tbsp per cupcake. Bake for 18 to 21 minutes on the center rack. (If your oven has hot spots like mine does, I like to swap the tins from left to right and spin them around 90 degrees halfway through baking to get nice even cupcakes.)
Allow the cupcakes to cool in the pans for 15 minutes, then remove them to a wire rack to cool completely. Once cool, arrange the cupcakes into the number 24 on a cake board or large platter.
Meanwhile, scoop the icing into a large bowl (or stand mixer). Add the powdered sugar and mix on low speed until incorporated. The icing should form peaks that keep their shape. (See note 2.) Transfer most of the icing to a piping bag fitted with a large star tip.
Add a small dot of icing to the bottom of each cupcake to keep it in place. Pipe large rosettes on each cupcake starting with the outer edge and swirling in toward the center. As you start each cupcake, try to get the icing to touch the edge of the previous cupcake's rosette to limit gaps.
Swap the tip for a smaller one or use a separate piping bag. Transfer the remaining icing to the piping bag with the small tip and fill in gaps by making dots, kisses or other shapes. Add smaller rosettes on top of the large ones you already piped to add height and visual interest.
Finally, decorate with sprinkles.