This French onion soup–inspired recipe takes stuffed mushrooms from hors d’oeuvre to elegant vegetarian main course. While sliced onions caramelize on the stove, portobello mushrooms roast and bread cubes toast in the oven. Layer the onions, bread, and some Gruyère cheese in the roasted mushroom caps and broil until golden brown.
Game plan: The onions can be caramelized and cooked with the sherry up to 2 days ahead. Refrigerate in a covered container and reheat on low before stuffing the mushrooms.