Preheat oven to 400ºF.
Cut about a quarter of an inch off the top of the garlic head and place it onto a square of aluminum foil. Drizzle with about 1 tablespoon EVOO and close the foil up around the garlic. Transfer to the oven and roast until golden brown and tender, about 40 minutes. Remove from the oven and let cool.
While the garlic is roasting, place a large skillet over medium heat with 1 turn of the pan of EVOO, about 1 tablespoon, and the butter. Add the onions, bay leaf and thyme to the pan and cook gently until the onions are well caramelized, about 30 minutes. Season with salt and pepper, and reserve.