Swiss Chard, Fennel, And White Bean Gratin

Ingredients

• 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)