Heat the can well to melt the fat and carefully transfer the duck legs on a tray. Bake in a preheated oven at 220°C for 15 minutes. Turn the oven to grill/broiler mode and bake for another 5 minutes until the drumsticks are golden brown and the skin is crispy. You can transfer the remaining duck fat from the can to a jar or food container, close it well and store in the refrigerator for later uses.
In a shallow pot, heat up 4-5 tbsp of the duck fat and fry the diced onion and sliced garlic for 2-3 minutes. Add the carrot cut into thin crescents. Season with salt, pepper, cover with a lid and cook for 8-10 minutes over medium-high heat until the vegetables are tender.
Prepare a bouquet of herbs, tie with cotton thread and place in the cooking pot. Add the leeks cut into rings, the coarsely chopped potato, stir and add the lentils. Pour in the stock, cover and cook over medium heat for 25-30 minutes, until the lentils are cooked, but do not overcook them. Then remove the herbs and mash the potatoes with a fork.
Place the lentils on a serving plate and place a duck leg on top. Sprinkle with finely chopped parsley and serve immediately.