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The Le Creuset type of pot has several very attractive properties. It is heavy and conducts and holds heat very evenly (like a cast iron skillet or baking dish), It is suitable for use both on top of the stove (on a burner) or inside the oven. The porcelain finish gives it significant non-stick properties and prevents the cast iron beneath from absorbing flavors (actually one of the attributes of normal cast iron cookware called "seasoning"). It allows the use of acidic foods or liquids without damage and there are no metals or impurities to leach into the food you are cooking. It also makes the cookware available in a variety of attractive colors making it suitable for going from the oven to the table. Add to that the fact that the cookware because of its cast iron center holds heat exceptionally well and you have what many consider the perfect oven to table serving dish as it will generally keep food warm throughout a meal.
The even cooking this design provides makes it particularly attractive for dishes that require long slow cooking (braises, many casseroles, stews, chili's, etc.) It will also stand up to very high heats and is very good for dishes that require that you brown or sear meat quickly on top of the stove and then cook for an extended time in the oven as this design allows you to do both in a single dish. The porcelain finish makes clean up easy and helps prevent food sticking and its acceptance of high heat makes it easy to deglaze a pot (for example after cooking a roast beef and removing it from the pot, you often want to get the meaty bits and fat that has stuck to the bottom of the pan loose so as to produce a gravy and richen it with the same flavor profile as your seasoned the beef. You can do this by placing the hot pot on a burner, adding wine and high heat which liquifies and loosens the tasty morsels. In the same pot you can then reduce the wine and remains. And then because of the protective porcelain surface you can use a steel gravy whisk inside the same pot to break up any lumps which might occur when you add stock or water and the beurre manie without damaging or scratching the pot as the porcelain is harder than the steel). For the same reason, unlike with most other non-stick cookware you can also freely use steel spoons and spatulas without damaging the cookware.
There are many other brands of porcelain covered cast iron cookware similar to the brand name Le Creuset but the quality varies significantly. You should note also that Le Creuset in addition to making porcelain covered cast iron cookware also makes a line of baking ware that is not suitable for the above listed tasks as it is purely bakeware and is designed to work inside the oven and not on top of the stove. The easy way to tell whether a Le Creuset dish you are examining is the cookware or the bakeware is the weight. The cast iron coated with porcelain is very heavy while the bakeware for the same size dish is much lighter.