How to Make It
Preheat the broiler. In a large skillet, melt the butter with 2 tablespoons of the honey over moderately high heat until foaming. Add the plums and cook, turning occasionally, until softened and the honey has thickened slightly, about 6 minutes. Scrape the plums and their juices onto a plate.
In a medium heatproof bowl set over a saucepan of simmering water, whisk the egg yolks, Moscato and the remaining 1/4 cup of honey until the mixture is thick and pale yellow, about 8 minutes. Remove from the heat and whisk the sabayon until cooled slightly, about 1 minute.
Scrape the sabayon into four 8-ounce gratin dishes. Top with the plums and their juices. Transfer to a baking sheet. Broil 3 inches from the heat for about 1 minute, until the sabayon is golden, and serve.