Sunchoke (Jerusalem Artichoke) and Leek Soup with Mushrooms

Ingridients of Sunchoke (Jerusalem Artichoke) and Leek Soup with Mushrooms:

• 2 tablespoons olive oil
• 2 large leek, halved lengthwise and thinly sliced crosswise
• 6 sunchokes, roughly chopped
• 3 stalks celery, chopped
• 1 large carrot, chopped
• 3 cloves garlic, minced
• salt and ground black pepper to taste
• 2 bay leaves
• 1/2 bunch fresh tarragon, chopped
• 1 dash vermouth
• 5 cups vegetable broth
• 2 bunches watercress
• 2 tablespoons butter
• 2 cups chopped fresh mushrooms
• 1/2 bunch fresh tarragon, chopped