Step 1

Heat oven to 450 degrees. Wrap garlic in aluminum foil, and cook until soft, about 45 minutes. Set aside until cool enough to handle. Cut off the top of garlic head, and squeeze flesh into a small bowl; set aside.

Step 2

Cut off top quarter from each onion, and wrap each onion in aluminum foil. Cook onions until soft, about 1 1/2 hours.

Step 3

Remove onions from oven, unwrap, and let cool 15 minutes. Peel, and discard skins. Working from the center of each onion, pull out all but two outer layers, leaving a shell. Place shells in a small baking dish. Measure 3 cups of onion flesh.

Step 4

Place half of the onion flesh in the bowl of a food processor. Add basil, parsley, reserved garlic flesh, 1 teaspoon salt, and 1/8 teaspoon pepper. Puree, and set aside.

Step 5

Bring a large saucepan of water to a boil. Peel potatoes, and cut into 2-inch cubes. Cook potatoes until fork tender, about 20 minutes; drain in a colander.

Step 6

Pass potatoes through a ricer set over a large bowl. Slowly whisk in pureed onion mixture. Set potato filling aside.

Step 7

Coat a small saute pan with cooking spray, and set over medium heat. Add one variety of mushroom. Season with remaining 1 1/2 teaspoons salt and 1/8 teaspoon pepper; cover. Cook, stirring occasionally, until tender and slightly golden. Transfer mushrooms to a bowl. Repeat cooking process with remaining mushrooms. Roughly chop remaining onion flesh; stir into mushroom filling.

Step 8

Stuff onion shells with alternating spoonfuls of potato and mushroom fillings. Spray with cooking spray. Add wine to baking dish.

Step 9

Bake stuffed onions until they are soft and golden, about 30 minutes. Let onions cool slightly, and serve warm.