Dark-Chocolate Frosting Shots

In a microwave-safe bowl, microwave the chocolate at high power in 10-second intervals until just melted. Let stand until cooled to room temperature, about 15 minutes.

In a standing electric mixer fitted with the paddle, beat the butter with the salt at medium speed until fluffy, about 2 minutes. At low speed, beat in the confectioners' sugar, 1/2 cup at a time, then beat in the vanilla. Add the cooled chocolate and beat at medium speed until fully incorporated, scraping down the bowl as needed. Scrape the frosting into a piping bag fitted with a star tip and fill small paper cups with 1 tablespoon of the frosting; serve.