Preheat oven to 375°F.
Add melted butter to bread crumbs and cheese in a bowl, mix well and set aside.
In a medium to large stockpot, Sauté onion in olive oil and cook over medium heat until onion starts to carmelize.
Meanwhile remove green parts from swiss chard (just rip off the leaves) and reserve the stems. Split thick stems in 2 and chop like celery into ½ moon pieces about ½” wide. Then chop leaves roughly – keep stems and leaves separate. Add chopped stems to carmelized onions and when then start to slightly reduce add leaves in two batches mixing well. Add optional sour cream or crème fraiche or cream and mix well. Season. Do not over cook! Leaves should be steamed but not lose their color! You want your leaves to be green!
Dump contents of stockpot into a gratin dish and top with reserved breadcrumbs mixture. Bake until breadcrumbs are golden brown 15-20 mins.
Note about cheese: Go wild! I’ve used pecorino, fontina, parmagiana, gouda, mimolette…what every you have you’d like to use up, and don’t be afraid to mix your cheeses.