Soak the lid and the base in water for at least 2 hours, or overnight. As some clay cookware is quite large, you may need to get creative. Use a large bucket, a bathtub, a sink, a laundry room washbasin, a plastic basin. If you can’t find something large enough to accommodate the top of a tagine, invert the tagine lid and fill it with water instead.
Drain the water and dry the tagine (or other clay cookware). If the cookware is unglazed, rub the interior and exterior of the lid and base with olive oil.
Place the tagine or other clay cookware in a cold oven. Turn the oven on to 300° F (150° C), and set the timer for 2 hours.
After 2 hours, turn off the oven, and leave the tagine to cool completely in the oven. Wash the cooled tagine by hand, and coat the interior with olive oil before storing or using.
Authentic Moroccan clay and ceramic tagines will crack if subjected to high heat. (The same applies to other types of clay cookware.) Unless otherwise directed, use a low burner setting or an oven temperature of no more than 325° F (160° C), and wait patiently for the tagine to reach a simmer. Heat diffusers are recommended for cooking on a burner.
Tagines and other clay cookware may also crack if subjected to rapid changes in temperature. Avoid this by not adding cold food or liquids to a hot tagine, and by taking care not to place a hot tagine on a cold surface. Similarly, don’t add hot liquids to a cold tagine, or place a cold tagine in a preheated oven.
Hand wash your tagine with very mild soap, baking soda or vinegar, and rinse well. Leave the tagine to dry thoroughly, and then lightly coat the interior of the lid and base with olive oil before storing.
It’s a good idea to store your tagine with the lid slightly ajar so that air can circulate. I find that glazed ceramic tagines have a tendency to mold, and this will help prevent that. If the interior does develop a little mold, simply wash the tagine and lightly coat it with olive oil before using.
Some darkening or staining should be expected with the use of a tagine; this is a desirable characteristic. According to Moroccan cookbook author Paula Wolfert, you can speed up this darkening by “curing” the tagine instead of just seasoning it. This can be done by rubbing ashes along with oil on the tagine, and then leaving the tagine in a slow oven for eight hours or longer. Sounds messy, but the tagine should take on a beautiful, aged look.