Rinse the belly of excess salt and the coarser spices.
Dry the water off with a tea towel and lay the belly out on the table.
Chop the onion and sauté it in a little oil for 5 minutes in a sauté pan, chop the parsley finely and mix it with the onions and continue to sauté for 2 minutes.
Remove the pan from the heat and mix in the grated nutmeg and a little salt and freshly ground pepper.
Let the mixture cool.
Then spread the mixture on top of the belly, roll it up like a roulade and tie the sausage with cotton string.
Place the rolled pork in a pot and pour cold water on it to cover.
Bring to a boil and skim off the impurities.
Add the rest of the spices and the celery, cut into coarse pieces, and simmer the rolled pork over low heat for about 1½ hours.
It should still be firm
Place the rolled pork in a rolled pork press or place it in a tray with a plate or a cutting board and something very heavy on top.
In both cases, pour as much of the cooking liquid over as possible, which will make the rolled pork juicier.
Put it in the refrigerator until the next day.