Take the lamb leg out of the fridge about 30 minutes before putting it in the oven.
2.5 kg leg of lamb
Preheat the oven to 120 degrees Celsius (248 degrees Fahrenheit).
Prepare the lamb leg by removing any visible tendons and membranes. Then, score the surface with a sharp knife. It's okay to cut into the meat a little.
Prepare the marinade for the lamb leg. Finely chop the rosemary, thyme, and garlic and put them in a small bowl with the olive oil, lemon zest, salt, and pepper. Mix well.
2 tbsp olive oil, 4 cloves garlic, 2 tbsp fresh rosemary, 2 tbsp fresh thyme, 1 lemon, 2 tsp salt, Pepper
Now, coat the lamb leg with the marinade and set it aside. You can do this the day before and refrigerate the lamb leg to allow the flavors to penetrate the meat. Take out a large ovenproof dish. Rinse the potatoes and cut them into quarters, then place them in the dish.
1.5 kg potatoes
Clean the fennel bulbs thoroughly as you would with leeks. There may be dirt, so it's important to be thorough. Cut them into quarters and add them to the dish with the potatoes.
2 fennels
Peel the garlic cloves and add them to the dish. Cut one lemon into slices and add them to the dish along with the juice from 1/2 lemon.
1.5 lemon, 10 cloves garlic
Add olive oil, white wine, salt, and pepper to the dish, along with plenty of fresh rosemary and thyme. Mix everything together well.
3 tbsp olive oil, 3 sprig fresh rosemary, 3 sprig fresh thyme, 3 dl white wine, 2 tsp salt, Pepper
Place the lamb leg on top of the potatoes. Place the dish almost at the bottom of the oven and cook the lamb leg for about 4 hours or until the core temperature is 62 degrees Celsius (144 degrees Fahrenheit) at the bone. - I have an oven with a built-in thermometer, so I can monitor the temperature. I would recommend using a meat thermometer with a probe that can withstand the oven, as it makes everything much easier. Alternatively, you'll need to check the core temperature a few times during cooking. Once the core temperature is reached, turn up the oven temperature to 230 degrees Celsius (446 degrees Fahrenheit) with convection. Now, the lamb leg just needs about 10 minutes at high heat to brown the surface a little.
When you're satisfied, take the lamb leg out of the oven. Place it on a cutting board and let it rest uncovered for about 20-25 minutes before carving.
While the lamb leg is resting, continue cooking the potatoes in the oven at the high temperature. Stir it occasionally until everything has some color.
When the lamb leg has rested and the potatoes have a nice color, the dish is ready to serve.