Making a gratin d'oignons perlés à la crème requires two steps. First, braise the onions the way you would to cook pearl onion confit, then finish them in the oven as a gratin.
The pearl onion gratin is composed of pearl onions, crème fraîche, thyme, red chili flakes, nutmeg and parmesan. It's a nice accompaniment to poultry. I served it with the roasted pheasant stuffed with sage and Granny Smith apples I made for my 4-course French meal in honor of the movie "Julie and Julia".
One trick to making this dish look great is to use the right serving dish. I especially like these individual serving dishes, which I got from Staub.