3 large leeks (1 to 1 1/2 pounds), white parts only, cleaned and sliced 1/2 inch thick
2 garlic cloves, minced
3 large carrots (10 ounces), diced
1 celery stalk, diced
1 large or 2 medium turnips (10 ounces), peeled and diced
1 pound russet potatoes, peeled and diced
A bouquet garni made with a bay leaf and a few sprigs each thyme and parsley
Salt and black pepper
¼ cup crème fraîche, more to taste
Chopped fresh parsley or tarragon, for garnish