Place the pork belly on the counter and season it with salt and pepper and spread the mustard on the inside.
Remove the leaves from the thyme and sprinkle them on the mustard.
Once the sauerkraut has cooled, squeeze it well so that most of the moisture is out and spread the squeezed sauerkraut over the meat.
Now roll up the meat and tie it with butcher's twine.
Put a knob of butter in the roasting pan and fry the roulade all around until it is nicely colored. Then put the roulade in an oven dish and put it in a preheated oven at 170℃ until the core is 70℃. This takes about 45 minutes. Remove the roulade from the oven and let it rest for at least 15 minutes before you cut it.