In a large pot, heat 2-3 Tablespoons butter over medium heat. Add 1 large chopped onion and 3-4 leeks. Sauté 5 minutes, or until they become tender.
Stir in 2 cloves garlic and cook 1 to 2 minutes, being careful not to let it brown.
Simmer. Stir in 1 1/2 pounds potatoes, 2 bay leaves, and 1/2 teaspoon thyme. Pour in 4-5 cups broth. Season with salt and pepper (I start with about 1/2 teaspoon salt and 1/4 teaspoon pepper). Bring to a boil and then reduce the heat to low. Cover and simmer 15 to 20 minutes.
Blend. Once the potatoes are tender, remove pot from the heat. Remove the bay leaves. Using an immersion blender, puree until smooth, or blend portions of soup in batches in a blender before returning to the pot.
Slowly stir in the heavy cream. Simmer on low heat 5 minutes to let the flavors meld together.
Season the soup with salt and pepper. Ladle into bowls and serve with desired toppings.
Notes
Storage: Let the soup cool to room temperature before transferring to an airtight container. It will stay fresh up to 3 to 4 days in the refrigerator.