This is a modern, from-scratch take on a classic casserole. We're not going to pretend it's healthy, though you could make it lighter by subbing milk or nonfat yogurt for the heavy cream. I made a big dish of it for some friends who just had a baby — it's that kind of easy comfort food. Its use of tuna makes this a friendly dish during Lent, though if you don't like the fish or feel weird about it in a hot casserole, you could easily use cooked chicken instead (about 2 cups' worth). You could also leave the meat out altogether and create a mushroomy macaroni and cheese of sorts.
Michelle Stark, Times food editor