makes a generous 3 cups; enough to frost a layer cake (6, 8 or 9 inches) or 24 cupcakes
(recipe adapted from originals by Alice Medrich and Meg Ray)
Melt chocolate in stainless steel bowl set over simmering water. Remove bowl from water and set aside to cool.
Using the whisk attachment on a stand mixer, whisk egg yolks until they thicken and turn very light yellow. Toss in the pinch of salt. You can't over-mix, so just let the mixer run on medium while you do the next step.
Combine the sugar and water in a small saucepan and set on the stovetop over medium heat. Bring to boil and cook, without stirring, until sugar is dissolved and temperature reaches soft-ball stage on a candy thermometer (225°–230°F at 5000 ft. elevation, 235°–240°F sea level).
Turn mixer speed to low and drizzle the boiling sugar syrup into the egg yolks, then increase to medium, and beat until cooled to room temperature.
Now it's time to add the butter, one tablespoon at a time, while keeping the mixer on medium speed and beating after each addition until it is absorbed into the yolks. Adding the butter and mixing to a beautifully creamy frosting will take several minutes. Don't panic if it looks curdled as you add the butter, just keep mixing and it will be fine in time.
Drizzle in the cooled, melted chocolate and beat 30 seconds. Now you're ready to frost!