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1
Combine egg whites, sugar, and salt in the heatproof bowl of a standing mixer set over a pan of simmering water.
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2
Whisk constantly by hand until mixture is warm to the touch and sugar has dissolved (the mixture should feel completely smooth when rubbed between your fingertips).
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3
Attach the bowl to the mixer fitted with the whisk attachment.
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4
Starting on low and gradually increasing to medium-high speed, whisk until stiff (but not dry) peaks form.
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5
Continue mixing until the mixture is fluffy and glossy, and completely cool (test by touching the bottom of the bowl), about 10 minutes.
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6
With mixer on medium-low speed, add the butter a few tablespoons at a time, mixing well after each addition.
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7
Once all butter has been added, whisk in vanilla.
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8
Switch to the paddle attachment, and continue beating on low speed until all air bubbles are eliminated, about 2 minutes.
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9
Scrape down sides of bowl with a flexible spatula, and continue beating until the frosting is completely smooth.
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10
Keep buttercream at room temperature if using the same day, or transfer to an airtight container and refrigerate up to 3 days or freeze up to 1 month.
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11
Before using, bring to room temperature and beat with paddle attachment on low speed until smooth again, about 5 minutes.
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12
(Optional) To tint buttercream (or royal icing), reserve some for toning down the color, if necessary.
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13
Add gel-paste food color, a drop at a time (or use the toothpick or skewer to add food color a dab at a time) to the remaining buttercream.
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14
You can use a single shade of food color or experiment by mixing two or more.
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15
Blend after each addition with the mixer (use the paddle attachment) or a flexible spatula, until desired shade is achieved.
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16
Avoid adding too much food color too soon, as the hue will intensify with continued stirring; if necessary, you can tone down the shade by mixing in some reserved untinted buttercream.
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17
Using a flexible spatula, fold 4 1/2 ounces semisweet chocolate, melted and cooled (see page 323), into buttercream mixture in step 3, along with the vanilla extract.
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18
Mix 2 tablespoons good-quality instant espresso powder (do not use instant coffee) with the vanilla extract, and add in step 3.
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19
Split 1 vanilla bean lengthwise and scrape seeds into a food processor (reserve pod for another use); pulse with the sugar in the recipe until combined, then pass through a fine sieve to separate the larger pieces (discard these).
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20
Heat vanilla-bean sugar with the egg whites in step 1.
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21
Beat in 1 container (6 ounces) fresh raspberries (or other berries) after all butter has been added, until buttercream is streaky (do not overbeat).
