Ina Garten Potato, Fennel & Gruyère Gratin. You'll Need: potatoes, onion, fennel bulbs, olive oil, butter, heavy cream, Gruyere cheese, salt, and pepper. Carrisa Says - used one large fennel bulb instead of two small. Turned out wonderful! Hubby loved it! Definitely a keeper. Variation to try: nix fennel and add 50:50 potatoes and rutabega, and add 2 cloves of garlic.