Purée of Winter Vegetable Soup

Name: Purée of Winter Vegetable Soup
Ingredients: 1 tablespoon extra virgin olive oil; 1 medium onion, chopped; 1/2 pound leeks (1 large or 2 small), white and light green parts only, cleaned well and sliced; 1/2 pound carrots (2 large), peeled and sliced; 1/2 pound kohlrabi, trimmed, peeled and diced; 1/2 pound turnips, peeled and diced; 6 ounces potatoes (2 medium), peeled and diced; 1 1/2 quarts water, chicken stock or vegetable stock (see note); 2 fat slices ginger, peeled; 1 bay leaf; A couple of sprigs each thyme and parsley; 12 peppercorns; Salt and freshly ground pepper to taste