5 tablespoons unsalted butter
1 large bulb fennel, cored, and sliced thin (about 3 cups)
1 large onion, sliced thin (about 1 1/2 cups)
Kosher salt and freshly ground black pepper
3 medium cloves garlic, minced (about 1 tablespoon)
3 bunches swiss chard (about 1 pound), leaves removed, tender stems sliced thinly
1/2 teaspoon freshly grated nutmeg
1 tablespoon flour
1 1/2 cups half and half
2 (15 ounce) cans white beans, drained and rinsed
1 1/2 cups fresh breadcrumbs
2 ounces finely grated parmesan or romano cheese (about 1 cup)