You can change the vegetable according to the season, but the method is always the same. The secret: Put the vegetables with the longest cooking time at the bottom of the tajine so they all cook evenly.
Slice the onion or leek into very thin slices. Put into a thick-bottomed casserole.
Slice the rest of the vegetables into long pieces that are more or less even.
Put the vegetables and spices in the casserole little by little, starting with the potatoes.
Add the olive oil and 2 Tbsp water.
Cover and place on medium-low heat until steam starts to come out from under the lid. Turn down the heat if necessary.
Continue cooking for about 30 minutes until the vegetables are starting to simmer in their own juices (of course the cooking time varies according to the vegetables and your taste- adjust accordingly).
Add the olives about 10 minutes before cooking is finished.
Serve hot or room temperature.