Basic Buttercream Recipe
For a chocolate variation, stir 4 oz melted and cooled chocolate (milk or dark chocolate work) into the buttercream after you add the butter.
2. Simmer5 minutes
Heat about 2” of water in a small pot and bring to a simmer.
3. Dissolve2-3 minutes
Meanwhile, combine sugar, egg whites, and salt in a large heat-proof mixing bowl (one that can be set over the small pot without touching the water). Set the bowl over simmering water, and stir constantly until the egg whites are warm to the touch and sugar is dissolved, about 2 to 3 minutes. If you are not sure if the sugar is dissolved, quickly dip a finger into the bottom of the mixture and feel for any grittiness.
4. Mix10 minutes
Using an electric mixer or a stand mixer fitted with the whisk attachment, beat the warmed egg whites on low speed until foamy. Once foamy, increase speed to medium-high speed until stiff, glossy peaks form and mixture is cooled completely, about 10 minutes. (Note: if your egg whites remain soupy and do not whip up at all after 5 minutes or so, you will have to start all over!)
5. Keep Mixing5-10 minutes
Switch to the paddle attachment if possible. Reduce speed to medium-low; add softened butter 2 tablespoons at a time, beating to incorporate fully after each addition. After all the butter has been incorporated, beat in vanilla. (Note: because of the water content of the butter, the mixture might seem like it has curdled after you start incorporating the butter but be patient! It takes time and the addition of even more butter and lots of air to fully emulsify the egg mixture and the butter).
Let stand, lightly covered, at room temperature until ready to use. If you are making this in advance, transfer the buttercream to airtight containers and refrigerate for up to 4 days or in the freezer up to 1 month. Before using, bring the buttercream to room temperature, then beat with paddle attachment on low until smooth.