• In the top of a double boiler, whisk together egg whites and sugar. Cook over simmering water, whisking frequently, until an instant-read thermometer registers 140°F (60°C).

Using an Ankarsrum Mixer:

• Carefully pour mixture into Ankarsrum beater bowl. Using the balloon whisks, beat at medium-high speed (6 o’clock) until meringue has thickened and cooled to room temperature, 3 to 5 minutes. Add butter, 1 tablespoon (14 grams) at a time, beating until combined after each addition. Beat in coconut oil, vanilla, and salt. Beat until buttercream comes together and is thickened. (Buttercream may look curdled at first, but keep mixing and it will soon emulsify.) Use immediately, or refrigerate in an airtight container for up to 1 week. When ready to use, let come to room temperature, add to the Ankarsrum beater bowl, and using the balloon whisks, beat at medium-high speed until fluffy.

Using a Conventional Mixer:

• Carefully pour mixture into the bowl of a stand mixer fitted with the whisk attachment. Beat at medium-high speed until meringue has thickened and cooled to room temperature, 3 to 5 minutes.