Cooked Frosting
2 cups sugar
5 tablespoons plus 1 teaspoon all-purpose flour
2 cups milk
5 tablespoons plus 1 teaspoon heavy cream
2 cups unsalted butter, soft but cool, cut into small pieces
1 1/2 teaspoons pure vanilla extract
In a small heavy-bottomed saucepan, whisk the sugar and flour together. Add the milk and cream and cook over medium heat, whisking occasionally, until the mixture comes to a boil and has thickened, about 20 minutes.
Transfer the mixture to the bowl of an electric mixer fitted with the paddle attachment. Beat on high speed until cool. Reduce the speed to low and add the butter then beat until thoroughly incorporated. Increase the speed to medium-high and beat until the frosting is light and fluffy.
Add the vanilla and food coloring and continue mixing until combined. If the frosting is too soft, transfer the bowl to the refrigerator to chill slightly: then beat again until it is the proper consistency. If the frosting is too firm, place the bowl over a pot of simmering water and beat with a wooden spoon until it is the proper consistency.