In this recipe for stuffed onions, mild onion layers are filled with a tasty mushroom and Cheddar cheese blend spiked with sage and a splash of dry sherry. Serve as a vegetarian main dish for 4 or as a vegetable side dish for 8.
Preheat oven to 425°F. Coat an 8-inch-square baking dish with cooking spray.
Bring a large pot of water to a boil. Trim the ends off the onion and cut in half lengthwise; peel. Cook the onion halves in the boiling water for 2 minutes. When cool enough to handle, remove the 4 largest outer layers from each half. Return the remaining pieces to the pot and boil for 5 minutes more to cook through. Set aside. Using tongs, return the 8 onion layers to the boiling water and cook until soft and pliable, 1 to 4 minutes, pulling each layer out as it’s done. Set aside on a plate.
Heat butter in a large nonstick skillet over medium heat. Add shallots and garlic; cook, stirring, until the shallots are soft, 4 to 5 minutes. Add mushrooms and 1/4 teaspoon each salt and pepper. Add sherry (or wine); cook, stirring, until almost all the liquid has evaporated and the mushrooms form a soft mass, 8 to 10 minutes. Stir in 2 teaspoons sage; cook 30 seconds more. Transfer the mixture to a medium bowl; stir in cheese, breadcrumbs, parsley, Worcestershire and Tabasco. Finely chop the reserved onion core; add to the bowl.
To stuff an onion layer, hold it with the curved side cupped in your hand. Spoon 4 to 5 tablespoons of stuffing into the center and gently form it into a football-shaped packet. Lay the packet seam-side down in the baking dish and repeat with the remaining layers. Brush the packets with oil and sprinkle with the remaining 2 teaspoons sage and 1/8 teaspoon each salt and pepper. Cover the dish with foil.
Bake until the onions are bubbling, 15 to 25 minutes. Serve hot or warm.