1/4 cup (½ stick/2 ounces/57 grams) butter, softened
2 cups (250 grams) powdered sugar
¼ teaspoon salt
1 ½ teaspoons vanilla, preferably Nielsen-Massey
4 tablespoons warm water
In a medium bowl, heat the butter in the microwave until just melted. Whisk in the powdered sugar, salt, vanilla and water until smooth.