Swiss Meringue Buttercream Recipe
In a medium pot, add at least 1-inch of water and bring to simmer.
Thoroughly wash and dry the stainless steel mixing bowl from your stand mixer (you don't want grease touching meringue). Add 7 egg whites and 2 cups sugar and whisk together. Place mixing bowl over a large saucepan of barely simmering water, creating a seal over the pot (bowl should be over the steam, not touching water). Whisk constantly until mixture reaches 160˚F (takes about 3 min). Sugar should be fully dissolved (you should not feel any sugar granules when rubbing mixture between finger tips). Mixture will feel hot to the touch.
Wipe water from bottom of mixing bowl and transfer bowl to stand mixer fitted with whisk attachment. Beat on medium-high speed until stiff glossy peaks form (about 15-20 min) and bottom of the bowl feels completely at room temp and not warm (important: warm meringue will melt the butter).
Once bowl is at room temp, switch to paddle attachment, reduce to medium speed and add butter 1 Tbsp at a time, adding it just as fast as it is absorbed by meringue. Once all butter is in, scrape down the bowl and continue beating until it reaches a thick whipped consistency (3 min on med-high speed). If it looks lumpy or liquidy at all, keep beating until smooth, thick and whipped.
Add 2 tsp vanilla extract and 1/4 tsp salt and mix on med-high until incorporated (about 1 min).
*Butter should be softened at room temp for about 1 hour (more or less depending on your room temperature). It should be slightly cool to the touch and not overly soft or warm. If too soft, refrigerate for 10 minutes at a time.
Troubleshooting: If your frosting seems soupy, or won't thicken up properly, this is usually due to the meringue or butter being too warm. See the Common Questions section above to troubleshoot.