Add butter to the bowl of a stand mixer fitted with the paddle attachment. Mix at medium speed for 2 to 3 minutes, or until it starts to lighten up in color and turn fluffy.
Stop the machine and scrape down the sides of the bowl with a rubber spatula. Add 1 cup confectioner’s sugar at a time until it has all been incorporated. Add milk, vanilla and salt and continue to mix until the mixture is very light and fluffy, about 1 to 2 minutes.
Use immediately, or store in the fridge, tightly wrapped for up to 3 days. Let come to room temperature and re-whip before using.
Notes
Frosting should cover a 9 x 13 sheet cake, a two 9-inch round layer cake, or 24 cupcakes.Storage: Store buttercream covered in the fridge. To reuse, bring to room temperature and rewhip for the best consistency.Sift the sugar. Sometimes sifting feels like a lot of work, but in this case, I strongly suggest that you don’t skip it. This is what will ensure your frosting is light, fluffy, and smooth. Use room temperature butter. This is very important when making frosting because room temperature butter can hold air and makes the final frosting more light and airy, whereas warm or melted butter will create a denser result.Mix up the Flavors. Swap the vanilla extract for citrus zest, peppermint extract, or almond extract based on what you are using it for!Add food coloring. I like to use natural food dyes and add a few drops depending on what the occasion is to transform the frosting color into something special.Make a chocolate frosting. Add in a ½ cup of sifted unsweetened cocoa powder to the powdered sugar before adding it to the butter. You can adjust the milk if needed for the right consistency.Try it dairy-free. Substitute the butter and milk for their dairy-free plant-based alternatives.