-
1
Cream the butter on medium speed, 3 to 5 minutes, in a standing mixer or with a hand mixer until soft, about 30 seconds. Add the sugar and beat on high speed until light and fluffy, 5 to 7 minutes.
-
2
In a small saucepan, combine 1/4 cup of the milk, the flour, and the vanilla extract, and whisk until there are no lumps. Over medium heat, slowly add the remaining 3/4 cup milk, whisking constantly, and cook until the mixture comes to a low boil. Then reduce the heat to low and keep whisking for a few more minutes, until the mixture starts to thicken.
-
3
Immediately remove the pan from the heat, but keep stirring. (After you have removed the pan from the heat, the mixture will continue to cook for a minute or two on its own. If you overheat it and get small lumps, try to whisk vigorously to get them out, or pass the mixture through a fine-mesh sieve.) If necessary, place the pan over a bowl of ice water to stop the cooking process and allow the mixture to cool.
-
4
Once the milk mixture has thickened, set it aside to cool to room temperature. You can stick it in the freezer to rush the cooling.
-
5
With the mixer on low speed, slowly pour the milk mixture into the butter-sugar mixture. Increase the speed to medium and beat until the frosting is light and fluffy, 3 to 5 minutes. Add vanilla to combine.
-
6
This version works beautifully as a filling with a dark-chocolate frosting-you get the best of both worlds: Dissolve 1 heaping teaspoon instant espresso powder in 1 tablespoon boiling water. Combine with the butter-sugar mixture.
-
7
This light and fluffy chocolate frosting tastes like whipped cream with a hint of chocolate: While the milk mixture is cooling, melt 4 ounces unsweetened or dark chocolate in the top of a double boiler set over simmering water, or in 30-second bursts in a microwave. Cool to room temperature. With the mixer on low speed, combine the chocolate with the butter-sugar mixture.
