Italian Meringue Buttercream
from ButterYum
makes 4-5 cups
enough to frost an 8-inch cake or 24 cupcakes (I always make extra, just in cast - it freezes beautifully)
Ingredients
5 large egg whites (150g)
1 1/4 cups granulated sugar (250g)
1/4 cup water
1 1/2 teaspoons pure vanilla extract
1 pound unsalted butter, room temperature (454g)
Directions
In a small, heavy bottomed sauce pan, make the sugar syrup by heating the water and sugar to 248-250F (this will take 5-10 minutes).
While the sugar syrup is heating, whip the egg whites on medium speed in the bowl of a stand mixer until soft peaks form. Be sure the bowl has no traces of fat (oil, butter, egg yolks, etc).
Shortly before the sugar syrup reaches the target temperature, increase the mixer to high and whip whites to stiff peaks (turn off mixer if the sugar syrup hasn't reached 248-250F yet).
When the sugar syrup is ready, lower the mixer speed to low and carefully pour the hot syrup into the whipped egg whites - pour just between the sides of the bowl and the whisk, being careful not to allow the syrup to hit the spinning whisk.
Increase the mixer speed to high and whip until the meringue has cooled completely (check by feeling the bottom of the bowl).
Once the meringue has cooled completely, slowly add the butter, 1 tablespoon or so at a time, until all the butter is fully incorporated. If the mixture starts to look curdled or "broken", see notes below.
Beat in the vanilla and prepare to indulge!!
Notes
A thermometer is essential - use either a candy thermometer or a digital instant read thermometer.
Do not place the thermometer in the sugar syrup until the sugar has completely dissolved (to prevent recrystallization). Also, while the sugar syrup is heating, you may wish to periodically wash the sides of the saucepan down with a silicone pastry brush dipped in water to prevent splashes from recrystalizing on the sides of the pan (which can make the entire batch of sugar syrup crystallize).
Use egg whites from shelled eggs, not egg whites from a carton (they do not whip well).
Be sure to use unsalted butter.
Buttercream should be served at room temperature.
Buttercream will develop tiny air bubbles upon standing so you may need to rewhip it occasionally to restore its smooth consistency.
To tint, use gel or paste colors for best results.
Butter is yellow so real buttercream will have a slightly yellow-ish cast, but the more air you whip into it, the whiter it will look. You may choose to flavor your buttercream with clear vanilla extract. For very white buttercream, you may choose to add bright white food coloring (also recommended to keep some shades, like pink or blue, from looking orange or green).
Be sure the egg white and sugar syrup mixture (aka meringue) has cooled completely before you start adding the butter. You can speed this process along by attaching a water jacket filled with ice to the stand mixer. If you don’t have a water jacket attachment, try placing bags of frozen vegetables around the outside of the bowl.
When adding the butter, If the mixture looks curdled or "broken" at any time, don’t panic - continue beating until it smooths out before adding more butter (if the mixture or your kitchen is too warm, a short rest in the fridge may be necessary).
Store Italian Meringue Buttercream in an airtight container at room temperature for up to 3 days, chill for up to 10 days, or freeze for up to a year. Frozen buttercream should be thawed in the refrigerator overnight. Chilled buttercream should be allowed to reach room temperature and rewhipped to restore consistency before using.