Ratatouille is usually served as a side dish, but may also be served as a meal on its own (accompanied by pasta, rice or bread). Tomatoes are a key ingredient, with garlic, onions, courgette, aubergine, bell peppers, marjoram and basil, or bay leaf and thyme, or a mix of green herbs like herbes de Provence. There is much debate on how to make a traditional ratatouille. One method is simply to sauté all of the vegetables together. Some cooks, including Julia Child, insist on a layering approach, where the aubergine and the courgette are sautéed separately, while the tomatoes, onion, garlic and bell peppers are made into a sauce. The ratatouille is then layered in a casserole – aubergine, courgette, tomato/pepper mixture – then baked in an oven. A third method, favored by Joël Robuchon, is similar to the previous; however, the ingredients are not baked in an oven but rather recombined in a large pot and simmered. When ratatouille is used as a filling for savory crêpes or to fill an omelette, the pieces are sometimes cut smaller than in the illustration. Also, unnecessary moisture is reduced by straining the liquid with a colander into a bowl, reducing it in a hot pan, then adding one or two tablespoons of reduced liquid back into the vegetables.