Peel and halve the onions. Wash the roast pork ham, pat dry with kitchen paper and place in a large saucepan. Fill with water so that the roast is covered, add the onion halves and spices (2 bay leaves, 5 allspice grains, 5 juniper berries and 1 teaspoon black peppercorns), bring to the boil and simmer with a lid on for about 5 hours . Take out and let cool down well. Tip: It is therefore best to cook the roast one day in advance! For the bread dough, pour the baking mixture (500 g) with lukewarm water (375 ml) into a bowl and knead the dough slowly at first, then at the highest level until it loosens from the edge of the bowl. Cover the dough with foil and let rise in a warm place for about 45 minutes. In the meantime, preheat the oven to 200 ° C and cover a baking sheet with baking paper. Knead the dough again and roll it out on a floured surface approx. 1 - 2 cm thick, so that the surface is sufficient to wrap the roast in it. Pat the prepared pork ham roast dry with kitchen paper, place it in the center of the rolled-out dough and brush / brush with medium-hot mustard (2 tbsp). Brush / brush the edges of the dough all around with water and wrap / wrap the ham in the bread dough. Press the edges well and then place the wrapped ham on the baking sheet lined with baking paper. Now cover everything with a tea towel and let rise for another 30 minutes. Then put the tray in the preheated oven on medium heat and bake it at 200 ° C for about 60 minutes until crispy and brown. To make the bread dough nice and crispy, slide a tall tray with water (approx. 200-300 ml) into the bottom of the oven. Carry out a visual check frequently. After approx. 30 minutes, place a sheet of aluminum foil over it and use the grill function for the last 3 - 4 minutes without foil. Remove the ham in the bread dough, let it cool down a little and cut into slices with a very sharp knife (here with an electric knife!) For serving. Serve the ham roast in bread dough with a delicious mixed salad. Various barbecue sauces are enough.