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Many Moroccan tagine recipes, such as Chicken Tagine with Carrots and Potatoes, can be prepared in either a traditional clay or ceramic tagine as shown here, or in a pressure cooker or conventional pot. When the latter method is used, many Moroccans will refer to the resulting stew not as a tagine, but rather as marqa or gamila (or sometimes douaz). According to whom you're talking, all of the terms may be viewed as correct.
From a strictly traditional perspective, however, I lean toward the opinion that the word tagine should be reserved for dishes which are actually slow-cooked in the traditional vessel.
Now compare the photo on this page to the one accompanying the recipe for the marqa version of Chicken with Carrots and Potatoes. The tagine and marqa recipes are nearly the same in terms of ingredients, but clearly the appearance of the finished marqa is different (and less attractive, I must say) than the tagine, in part because a dish cooked in a pot must be plated, while a tagine's ingredients often are appealingly arranged prior to cooking and are likely to remain undisturbed until someone reaches in to take that first bite. Additionally, vegetables which are slow-cooked in a tagine have more texture and structure to them, in the same way that roasted vegetables will differ from boiled ones.
Many Moroccans alternate between cooking methods, depending on the time they have for preparing a meal – a tagine cooks slowly over low heat, so it takes longer; or desired result – a Moroccan stew prepared as marqa usually yields more sauce, which may be preferable when you need to stretch a meal or when those present like to dip their bread in sauce with every bite.
In my home, I alternate between using a tagine and a pressure cooker with no complaints from my family, but a clay tagine definitely offers an extra layer of flavor that is impossible to achieve with more modern cookware.
See Tips for Cooking in a Tagine and Tips for Using a Pressure Cooker for more clarification of the two cooking techniques.
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