With the rack in the middle position, preheat the oven to 200 °C (400 °F).
Slice the top of each garlic head. Place them individually on aluminum foil sheets and drizzle with 15 ml (1 tablespoon) of oil. Close the foil. Bake for 50 minutes or until the garlic is tender and caramelized. Press the cooked head of garlic to bring out the garlic purée. Set aside.
Meanwhile, in saucepan, brown the onion in the remaining oil. Deglaze with the wine and reduce by half. Add the broth and garlic purée. Bring to a boil and simmer about 5 minutes. Season with salt and pepper.