In the bowl of a stand mixer fitted with the paddle attachment, beat confectioners’ sugar, 6 tablespoons (90 grams) warm water, and meringue powder at low speed until well combined, stopping to scrape sides of bowl. Increase mixer speed to medium; beat until mixture is the consistency of toothpaste, 3 to 5 minutes. Add sparkling wine, 1/2 to 1 teaspoon (2.5 to 5 grams) at a time, until icing reaches “10-second” consistency. (A ribbon of icing drizzled on surface should take 10 seconds to sink back into icing.)

Transfer icing to a large shallow bowl; cover with a damp paper towel, and let stand for 20 minutes. Using a wooden pick, pop and fill as many air bubbles that rise to the surface as possible before using.