This is an ultra-smooth, not-too-sweet buttercream and my frosting of choice, not only because of its exceptional texture and flavor, but because it can be endlessly varied. You can add chocolate, liqueurs, pureed fruits, juices, or even coffee. A stand mixer is best for this recipe, as it has to be beaten for quite a while; a candy thermometer is also helpful. It is crucial that any cake frosted with this buttercream be served at room temperature, or the texture and flavor will suffer.
The standard recipe below makes enough to fill and frost a three- or four-layer cake with lots of swirls and decorations on the outside. The large batch is the maximum amount that can be made in a 5-quart stand mixer.
For the Standard batch; makes about 6 cups
1-1/4 cups sugar
For the Espresso Variation:
2 tablespoons instant espresso powder (such as Medaglia d'Oro)
For the Large batch; makes about 7-1/2cups
1-1/4 cups plus 1/3 cup sugar
For the Espresso Variation:
2 tablespoons plus 2 teaspoons instant espresso powder (such as Medaglia d'Oro)
1. Place 1 cup of the sugar (if making a standard batch) or 1-1/4 cups of the sugar (if making a large batch) and the water in a small saucepan. Stir to wet the sugar. Bring to a boil over medium-high heat, swirling the pan occasionally. Dip a pastry brush in cold water and wash down the sugar crystals from the sides of the pan once or twice. Allow the sugar mixture to simmer gently as you proceed with the egg whites.
2. Meanwhile, place the egg whites in a clean, grease-free stand mixer bowl and whip until frothy on low speed using the balloon whip attachment. Add the cream of tartar and turn the speed up to medium-high. When soft peaks form, gradually add the remaining sugar. Continue whipping until stiff, glossy peaks form.
3. Bring the sugar-water mixture to a rapid boil and cook until it reaches 248°F to 250°F (120°C to 121°C). As the syrup cooks, check for visual clues to assess temperature: It starts out thin with many small bubbles over the entire surface. As the water evaporates, the mixture will become visibly thicker. The bubbles become larger and pop open more slowly. At this point, the syrup definitely looks thickened, but it has not begun to color; this is the firm ball stage. If you drop a bit of the syrup into a glass of cold water, it will form into a ball. When you squeeze the ball between your fingertips, it will feel firm.
4. When the syrup is ready, pour a thin, steady stream directly over the meringue. Do not pour any onto the whisk or the sides of the bowl. Whip the meringue until cool to the touch; this step is very important. With the machine running, add the butter a couple of tablespoons at a time. Keep beating until the buttercream is completely smooth.
5. The buttercream is now ready to use. Any flavorings may be added at this point.
Espresso Variation: The bitterness of coffee tempers the sweetness of the buttercream. Dissolve 2 tablespoons instant espresso powder (such as Medaglia d'Oro) in 2 tablespoons boiling water or warmed Kahlúa and add to the standard batch; add 2 tablespoons plus 2 teaspoons of each to the large batch. Whip well to incorporate. The coffee flavor can be adjusted according to your preference.
The buttercream may be refrigerated for up to 1 week in an airtight container or frozen for up to 1 month. If frozen, defrost in the refrigerator overnight and bring to warm room temperature before reheating. Always reheat before using.
Note: Temperature is key with this buttercream. If the meringue is warm when the butter is added, it will melt the butter and become soupy. If the butter is too cold, the buttercream will be lumpy and too firm. If your buttercream is too soft and loose, simply chill it over an ice bath. Chill for several minutes before proceeding. If the mixture is too stiff, just keep whipping; it might smooth out. You can also aim a hot hair dryer at the outside of the bowl; it will warm up the buttercream quickly. Or place a cup of too-firm buttercream in the microwave for a few seconds, then add it back to the larger amount to smooth out the overall texture.
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