3 potato leek and fennel gratin Recipes

butter, chopped leeks (white and pale green parts only; about 4 large), fresh fennel bulbs with fronds, trimmed, cored, thinly sliced, fronds reserved, red-skinned potatoes, peeled, thinly sliced, freshly grated parmesan cheese (about 4 1/2 oz), chicken stock or canned low-salt chicken broth, whipping cream

fennel bulbs, leeks, butter or 2 tbsp margarine, melted, salt, fresh thyme, chopped, baking potatoes, peeled and thinly sliced, all-purpose flour, salt, whipping cream, milk, gruyere cheese, shredded, fresh thyme, chopped, ground pepper