Put the egg whites in the bowl of a stand mixer fitted with a whisk attachment. Start the machine on medium-slow speed and whip until the eggs begin to get frothy. Turn the speed to medium.
Slowly add the sugar to the whipping egg whites, dropping the lemon juice in about halfway through the process.
When all the sugar is in, speed up the mixer and whip until stiff peaks form and the meringue is smooth and super shiny.
Turn the speed to medium-low and begin adding the butter. Add it bit by bit so the meringue doesn’t slop over the sides of the bowl. At this point, the meringue will fall and look ruined and broken. It’s not. This is what happens and it’s okay. If the meringue doesn’t fall, add a little extra butter until it does.
Turn the speed back up to medium-high and walk away. Come back in 10 minutes. Does it look like buttercream? No? Walk away and repeat until it does. If it still doesn’t look like buttercream after 30 minutes, add more butter until it does.
Use immediately, or cover and refrigerate for up to 1 week. Warm and rewhip the buttercream before using it if refrigerated.
There are a few things to be aware of with any meringue-based buttercream:
-- You can store it at room temperature for 24 hours; more than that and you need to keep it in the fridge.
-- If you’re not using it directly after making it, you always want to rewhip it right before use by beating it in the mixer with a whisk attachment and adding a bit of heat from a kitchen torch until it looks right.
-- If you’re planning on using the buttercream that has been kept cold, pull it out of the fridge about 2 hours before you intend to use it, whip and heat it, and then you’re ready to go.
-- Sometimes you’ll see people dip a spatula into hot water before icing a cake. This is wrong. If you heat the buttercream to the correct workable temperature, you won’t need a warm, wet spatula.
Swiss buttercream keeps for about a week in the fridge, but it’s always good to just make what you need when using an egg product.MORE
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