In the bowl of a stand mixer fitted with the paddle attachment, beat confectioners’ sugar and meringue powder at low speed until combined. Slowly add ⅓ cup warm water and vanilla extract, beating until fluid, about 1 minute. Increase mixer speed to medium, and beat until stiff, 4 to 5 minutes. Add water, 1 tablespoon 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 until ready to use. Using a wooden pick, pop and fill as many air bubbles that rise to the surface as possible before using. Store in an airtight container for up to 3 days.
Recipe by Victoria at https://victoriamag.com/royal-iced-sugar-cookies/