1. Heat the butter in a large (6-plus quart) stockpot or Dutch oven over medium heat. Stir in the leeks, Toasted Onion Herb seasoning and bay leaf. Sauté for 3 minutes.
2. Add in the potato. Cook, stirring occasionally, until the leeks and potatoes have begun to soften and brown slightly, about 5 to 8 minutes.
3. Pour in the vegetable stock, and bring to a boil. Reduce the heat to low, and simmer for 30 to 40 minutes uncovered, or until the vegetables are very tender.
4. Remove ½ of the potato-leek mixture and set aside.
5. Using an immersion blender, blend the remaining potato leek mixture until smooth. (If you prefer velvety soup, blend the entire mixture).
6. Add in the reserved potato leek mixture, heavy cream and lemon juice.
7. Ladle into bowls, and garnish with parsley. Top with crème fraîche and a dash of your favorite hot sauce.