For a sublimely delicious dessert that showcases seasonal fruits, this gratin is simply sensational. The custard sauce will require the majority of your efforts, although this can be made up to 2 days in advance. Arranging the fruit is a snap, and you can use whatever strikes your fancy. If you're pressed for time, assemble the gratins in advance and caramelize just before serving. If caramelizing is just one step too many, skip the sugar topping, and reheat the gratins under the broiler for 3 to 4 minutes.
Place the yolks and 1/3 cup of sugar in a metal mixing bowl and set the bowl over a pan of barely simmering water. Whisk vigorously until the mixture has thickened and the yolks are warm. At this point, the consistency of the custard should resemble a thick hollandaise sauce.
Add the scalded cream to the bowl and cook over barely simmering water for 20 to 30 minutes, whisking frequently. Be careful not to let the custard get too hot or the eggs will curdle. When the custard has thickened enough to coat the back of a spoon, strain into a clean, dry bowl.
Divide and artfully arrange the sliced fruit and berries on four ovenproof 7-inch plates. Pour 1/2 cup of the custard atop the fruit, sprinkle with nutmeg, and refrigerate the plates for at least one hour. If refrigerating longer, cover with plastic wrap.
Just before serving, evenly sprinkle one tablespoon of sugar atop each gratin. Place the plates on a cookie sheet and broil on a rack set closest to the flame. Carefully caramelize the sugar topping. You may also use a propane torch to caramelize the sugar; this method is faster, but the fruit and custard will not get especially warm. Serve immediately.