While the leeks cook, cut the carrots and parsnips crosswise into 1/2-inch-thick slices. The larger pieces can be cut in half again. Cut potatoes into 1 inch cubes. Precision isn’t essential here. Pile the vegetables into the pot with the leeks, mix, add the bay leaf and add enough chicken broth so that it comes just to the top of the vegetables. The amount may vary. Best to err on the side of less since you can always add more later. If you add too much, your soup with be thin.