A tajine, also spelled tagine, is a North African clay cooking vessel most often associated with Moroccan cooking. It can also refer to the type of dish you cook in a tajine. (Think casserole. It refers to both the type of dish you are cooking and the style of the cooking dish you are using. "I'm baking a casserole in a casserole.")
The concept behind both the clay vessel and the recipe is to produce a slowly braised dish cooked at lower temperature. The design of the tajine condenses all of the moisture under the lid allowing it to drip back down on the food for moist and tender meat and vegetables. This is an excellent solution for cooking tougher cuts of meat. Lots of aromatic spices and herbs are often used to add rich depth of flavour. Root vegetables and dried fruits also benefit from low and slow simmering and are often incorporated in sweet and savoury North African dishes. Any kind of stewing recipes are good candidates for a tajine, and a recipe for a tajine dish can easily be cooked in a Dutch oven or clay cooker.
Several cultures have a version of a braised dish and specialised cooking vessel. Interestingly, in Tunisia they have a similarly designed tajine but the dish they cook in it is more similar to a frittata. A ragout of meat, vegetables, and spices is placed in the bottom of the dish. Some form of starch is added like beans or potatoes. An egg and cheese mixture is poured oven top and the dish is baked until firm and crispy along the edges.
Traditional tajines are made of clay and can be glazed or unglazed. The knob-like top of the tajine makes it easy to grasp so that the lid can be removed to check on the contents. Historically, the centre of the knob was thinner and could be punched out. The cook would then place a fruit over the hole and would remove it to release some steam and regulate the cooking.
Beautifully decorated tajines are typically reserved as serving pieces and may only be suitable for low-temperature reheating of food. Simpler, larger tajines are designed for cooking. Recently, manufacturers have begun making tajines out of enamel-coated cast iron as well as various ceramics. Depending on the manufacturer and materials, they may be used in an oven, microwave, and/or on a stovetop. Always refer to the manufacturers' instructions.