Country French Garlic Soup

Ingredients:

2 whole heads of garlic, peeled
1 tablespoon olive oil
1 onion, finely chopped
2 tablespoons butter
6 cups chicken or vegetable broth
2 sprigs fresh thyme
2 bay leaves
Salt and pepper, to taste
4 egg yolks
1/2 cup grated Parmesan cheese
Crusty bread, for serving
Fresh parsley, chopped (optional for garnish)
Instructions: