Rinse leg of lamb cold and pat dry. Rub with salt and pepper. Place on a cold rinsed fat pan of the oven. Wash the herbs, dab dry and spread on the leg of lamb (put four stalks of thyme aside).
Peel a carrot and celery, clean the leek, chop everything into small pieces. Peel and quarter the onion. Arrange the vegetables and onion around the leg of lamb. Braise in the preheated oven (electric cooker: 175 °C/ gas: level 2) for about 1 1/4 hours.
In between, baste several times with your own gravy. In the meantime, roughly chop the olives, remaining thyme and washed parsley. Mix the dumpling dough with 375 ml water, add olives and herbs, allow to swell well.
Knead the dough again. Form 12 balls from the mixture, press flat and fry in hot fat for approx. 8 minutes, turning until golden brown. Keep the potato cookies warm. Peel the rest of the carrots and cut them into sticks. Cook in boiling salted water for about 10 minutes.
Drain (collect the cooking water) and allow to drain well. Caramelise the sugar in a pan until golden brown. Add the carrots, turn in it, add 8 tablespoons of cooking water, bring to the boil briefly.
Remove the leg of lamb from the fat pan, pour the gravy through a sieve into a pot, skim off the fat, fill up the gravy to 1/4 litre with hot water and bring to the boil. Stir in tomato paste and sauce thickener.
Season with salt and pepper. Slice leg of lamb, arrange on a plate with carrots and potato biscuits. Add the sauce.