Preheat oven to 400ºF.
Heat 1 1/2 TB olive oil in a large, heavy bottom pot over medium-high heat. Add the onions, salt, bay leaves, and rosemary. Cover pan, and cook about 5 minutes until the onions begin to appear translucent.
Remove lid, and cook over low or medium-low until the onions begin to brown and caramelize. Stir periodically while cooking.Tip: The lower the heat, the sweeter the onions will be (but it will also take longer!). Time Frame: This step will take anywhere from 1-3 hours, depending on the heat level and size of pot. Check on the onions occasionally-- stirring once an hour for low heat, once every 30 minutes for medium-low, until the onions begin to caramelize.
Meanwhile, cut the pointed tip off two heads of garlic. (Cut the top, not the end with the root.) Remove some of the outer papery skin.
Set garlic on a piece of aluminum foil, drizzle about 1/2 TB olive oil over the garlic heads, sprinkle with salt, and fold the foil over the garlic. Roast for 45-50 minutes, or until the garlic is golden.
Let the garlic cool slightly, and then push on the bottom of the garlic to remove the cloves. Set them aside.
When the onions begin to caramelize, add the garlic, and mash it with the back of a wooden spoon.
Add the broth (or wine), and stir-- scraping up any bits of onion stuck to the pan. Add the water, and bring to a simmer.
Taste broth, and add additional salt if needed. Remove the bay leaves.
If desired, pour gravy into a blender (or into the cup of an immersion blender), and blend until smooth. Serve warm.
Make Ahead:Refrigerate: Store in a sealed container, and use within 3-4 days.Freeze: Store in a sealed container, and use within 3-4 months.