Portobellos Stuffed with Herbed White Beans

Over the years I’ve accumulated a fairly extensive repertoire of vegetarian entrées, and we get more requests for them at the store every week. This is one of our favorites, and it works as a substantial side dish for a simple lamb or beef roast as well. I prefer to use Roman beans because they hold their shape well, but cannellini, cranberry, or even black beans would be good here, too.