From Cuisine Magazine, 1983

Beat butter in large bowl until fluffy; reserve. Heat maple syrup in heavy medium saucepan over medium heat to boiling; cook, without stirring, until syrup reaches firm ball stage or candy thermometer registers 244 F. 31 to 32 minutes, watching to see that syrup doesn't boil over. You should have about 1 cup.

When syrup reaches soft ball stage (238 to 240 degrees), after about 22 minutes, begin beating egg whites, with salt, in large grease-free bowl with clean beaters; beat, on medium speed, until stiff but not dry, 7 to 8 minutes. Continuing to beat, add hot syrup in thin stream, scraping down sides of bowl with rubber spatula once or twice. Continue to beat mixture until it has reached room temperature and bowl no longer feels warm, 10 to 15 minutes.

Increase speed to high; beat in one fourth of the reserved butter, about 1 tsp. At a time, then beat in remaining butter by tablespoonsful. Scrape down sides of bowl; beat in bourbon and vanilla. Enjoy!