Quick White Bean and Ham Gratin

This quick cassoulet-inspired gratin uses ham and cannellini beans instead of the duck, sausage, and traditional flageolets. The idea is to pull together a quick braise, top it with crisp bread crumbs, run it under the broiler, and serve. 

Variation: For an excellently smoky (and not at all traditional) fish version, use 8 ounces smoked salmon (first choice is the flaky hot-smoked kind, though lox is fine too) or smoked trout or whitefish instead of the ham. Instead of the tarragon, chop ¼ cup fresh dill.