Combine egg whites, sugar, and salt in the bowl of a stand mixer, and set the bowl over a saucepan containing 2 inches of barely simmering water
Whisk the egg whites constantly until the mixture is opaque and warm to the touch and registers about 120F on an instant-read thermometer for about 2 minutes
Transfer the bowl to the stand mixer and beat whites on high speed with the whisk attachment until it’s barely warm, registering about 80F, and the whites are glossy and sticky for about 7 minutes
Reduce the speed to medium-high and beat in the butter 1 piece at a time
Beat in cream of coconut and coconut and vanilla extracts. Stop the mixer and scrape the bottom and sides of the bowl
Continue to beat on medium-high speed until well combined, about 1 minute