Peel, wash and cut the carrots into pieces. Clean, wash and cut the leek into pieces. Peel and slice onions. Wash the meat, dab dry and cut the rind crosswise.
Rub the meat all around with salt and pepper. Place meat, vegetables, bay leaves and juniper berries on a fat pan of the oven and roast in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 2 hours.
Bring the stock to the boil and after about 50 minutes of baking time, deglaze the roast with it. Remove the fat pan from the oven, place the meat on a grid and let it drain, catching the gravy. Pour the gravy from the fat pan through a sieve into a pot.
Fill up with 500 ml of water and collected gravy, bring to the boil and stir in meat extract. Stir in sauce thickener, bring to the boil again. Season to taste with salt, pepper and sugar. Cut meat into 20 slices.
Cut open round pieces. Cover the lower halves with 2 slices of roast and pour sauce over each. Add the tops of the rounds.