The Easiest Italian Meringue Buttercream

Directions

1. Have a clean bowl (or mixer bowl of a stand mixer) near the stove with the strainer set over it.
2. In a 1-quart stainless steel bowl (because glass bowls are too slow to heat), mix the egg whites and water together thoroughly with a wire whisk. Whisk in the sugar and salt. Set the bowl in a wide skillet filled with enough hot tap water to reach above the depth of the egg mixture. Set the skillet over medium heat. Using a heatproof Silicone spatula, stir the egg mixture, sweeping the sides and bottom of the bowl constantly to prevent the egg whites from scrambling. Adjust the burner so the water remains below a simmer, and continue to stir until the mixture registers between 160° and 165° F on the instant-read thermometer. Swish the thermometer stem in the hot skillet water to rinse off the raw egg after each temperature reading.
3. Remove the bowl from the skillet and scrape the mixture into the strainer. Rap the strainer to coax the mixture through it, but do not press on any bits that may be left in the strainer. Turn the strainer and scrape the mixture clinging to the underside into the bowl. Beat at high speed for 3 to 4 minutes, or until the mixture is cool and resembles stiff fluffy meringue (which is exactly what it will be).
4. Cut the butter into several chunks and beat it into the meringue chunk by chunk, until it is smooth and creamy. The meringue will deflate when you add the butter. If the butter is too cold, the mixture will curdle or separate at first, but it will most likely smooth out as you continue to beat. If it remains curdled, set the bowl in a pan of warm water for a few seconds and then continue to beat. If the meringue or the butter are too warm when you combine them, the buttercream will seem soupy instead of creamy. If it doesn’t thicken up with more beating, set the bowl in a bowl of ice and water or in the refrigerator for 5 to 10 minutes, then resume beating until the mixture is creamy and smooth. Flavor as desired, with 1/2 teaspoon or more vanilla extract or vanilla bean paste, 3 to 4 teaspoons instant espresso powder dissolved in less than a teaspoon of water, grated citrus zest, etc. Avoid any flavoring that involves adding more than 2 or 3 teaspoons of liquid.
5. Refrigerate or freeze buttercream to store. To soften, break chilled or frozen buttercream into chunks with a fork. Microwave on low, for several seconds, then stir smooth with a rubber spatula. Or, set the bowl in hot water until some buttercream melts around the sides of the bowl. Stir, replace the bowl in the hot water, then stir again. Repeat until the buttercream is smooth and spreadable.
6. Note: This French-style buttercream is very different from American “buttercream” frosting made with confectioners' sugar and butter. If it is too thick or too soft, always adjust it by vigorous stirring and either gentle warming or chilling as necessary: Never adjust by adding more butter, sugar, or liquid.