Old-Fashioned Ermine Frosting

Directions

1. In a small heavy saucepan, whisk flour and milk until smooth. Cook and stir over medium heat until thickened and bubbly, 5-7 minutes. Remove from heat. Stir in sugar and salt until dissolved; transfer to a small bowl. Press plastic wrap onto surface. Refrigerate until cold.
2. In a large mixing bowl, beat butter until light and fluffy, about 5 minutes. Gradually beat in cooled milk mixture. Beat in vanilla. Switch to whisk attachment; continue beating on medium speed until frosting is stiff and fluffy. Frost cake immediately.