Wash the meat, dab dry and rub with salt and pepper. Put the meat into a large roasting pan and roast it in the preheated oven (electric cooker: 175 °C/ gas: level 2) for 3 1/2 hours.
Gradually add 1/4 liter of water. Pour roast stock over the meat several times. In the meantime, cut pumpkin into slices, peel and remove seeds. Cut the flesh into cubes. Clean, wash and cut leek into diagonal slices.
Peel and finely dice the ginger. Bring stock, vinegar and sugar to the boil in a pot. Cook the pumpkin for 15 minutes. Put it on a sieve, drain it and collect the broth. Add leek, ginger and peppercorns to the roast 20 minutes before the end of the cooking time.
During the last 15 minutes, cook the pumpkin. Pour on the sweet and spicy cooking liquid. Season vegetables with salt and pepper. Garnish roast with pepper panicles.