In the bowl, combine 2 cups confectioners' sugar, 4 ounces semisweet chocolate, 5 tablespoons unsalted butter, 1/4 cup water, 1 1/2 teaspoons pure vanilla extract, and 1/4 teaspoon kosher salt. Cook, stirring occasionally, until the chocolate and butter are completely melted, around 2 to 3 minutes. Remove from heat and stir until smooth and well blended, and use immediately.