Milk chocolate can be on the sweet side, so I added a little bittersweet to this recipe to tame it just a bit. Melt both chocolates, beat them together with butter and milk, then add some powdered sugar and a touch of vanilla. I’m not going to lie, the frosting’s still sweet, so spread it on less sweet cakes and cupcakes to balance out the flavors.
Game plan: This recipe makes enough buttercream to frost an 8-inch layer cake or 24 cupcakes.
Once made, let the buttercream sit at room temperature until you’re ready to use it, up to 3 hours. If you’re not going to use it within 3 hours, refrigerate it in a container with plastic wrap directly touching the surface for up to 3 days. To use refrigerated buttercream, let it sit at room temperature until softened, then beat it in the bowl of a stand mixer fitted with a paddle attachment until smooth and fluffy.