Preheat your oven to 400°F (200°C). Prepare a head of garlic by cutting the top off, drizzling it with olive oil, and wrapping it in aluminum foil. Place it in the oven and roast for about 30 minutes, or until the cloves are golden and soft.

In a large pot, heat a tablespoon of olive oil over medium heat. Add one chopped yellow onion and sauté for 5-7 minutes, stirring frequently, until the onion is translucent and slightly caramelized.

Once the garlic is roasted, allow it to cool slightly and squeeze the soft cloves into the pot with the onions. Pour in 4 cups of vegetable or chicken broth and add a few sprigs of fresh thyme. Stir everything together and bring the mixture to a gentle simmer for about 2 minutes.

Reduce the heat to low and let the soup simmer for an additional 15-20 minutes.

Remove the thyme sprigs and blend the soup using an immersion blender until it's perfectly smooth and creamy.

Return the pureed soup to low heat and stir in 1 cup of heavy cream, warming it through for about 5 minutes. Season with salt and freshly cracked black pepper to taste.

Ladle the soup into warm bowls, and garnish with fresh herbs or crunchy croutons. Serve with warm, crusty bread.