Clean the pork knuckle, salt, pepper. Place in a roaster with the stock and the onion, chopped coarsely or in wedges.
Cook open in the preheated oven at 160 ° C hot air (OU heat + 20 °) for approx. 2.5 - 3 hours. In between, pour the stock from the roaster over and over again. As soon as the stock has boiled off, pour in a little more water regularly.
At the end of the cooking time, lift out the pork knuckle - possibly grill over briefly if necessary.
Season the gravy with mustard, salt and pepper as desired and thicken with a sauce thickener if necessary. Serve immediately
You can also add carrots and celery to the stock from the start - although it is totally overcooked at the end, it gives the meat a totally different, delicious taste.