When you try this recipe, make sure your fruit pieces are all about the same size. This will allow you to roast it all at the same time. Also, when choosing apples and pears, look for firm green varieties.
Preheat oven to 400°F. On a baking sheet, combine grapes, plums, pears, apples, sugar and butter; toss to coat and spread out in a single layer. Bake until soft, about 15 minutes. Let cool.
In a large, stainless steel bowl, whisk together egg yolks and sugar. Set over a pot of simmering water (the bowl should not touch the water). Pour in wine and whisk vigorously to incorporate air until mixture has doubled in volume and is thick like whipped cream, about 10 minutes. You can use an electric mixer if it's easier.
Divide fruit among 6 dessert plates. Spoon sabayon over fruit. If desired, quickly wave a blowtorch over the surface to brown the sabayon.