The day before, soak the preserved lemons in a large bowl of water to remove some of the salt. Slice each wedge into 4 to 6 pieces.
Preheat the oven at 140 C / Gas 1. In an ovenproof pot, brown the veal on all sides in a little olive oil. Transfer the veal into a bowl and set aside. Deglaze the pot by adding a little water and scraping any cooked bits off the bottom of the pot; pour this sauce over the veal.
In the same pot, saute the onions for 5 to 6 minutes.
Add the veal, onions, lardons, preserved lemons, saffron, cumin seeds and lemon juice; cover with water, place a lid on the pot and braise in preheated oven for 4 hours.
After 2 hours, take the tagine out of the oven and taste the sauce. It should not be overly salty, because the sauce will reduce a little more during the next 2 hours. If in doubt, remove and reserve half the sauce with a ladle and replace with water. Return to the oven for another two hours.
Last tip regarding salt: If the dish is not salty enough, remove the veal from the pot and place in a serving dish. Heat the sauce and add some of the reserved salty liquid you removed earlier. When the desired taste is reached, pour over the veal and serve.