Place all spice rub ingredients into a small mixing bowl and toss together until well combined.
Place the pork belly on a clean surface, skin-side up and score the entire surface with a sharp knife, making sure not to cut into the meat. Pat both sides dry with a paper towel and set the pork belly, skin-side down.
Sprinkle the spice rub onto the pork belly and generously rub onto the entire surface of the meat.
Very tightly roll the belly into a log, making sure no gaps remain on the inside and tie roast with butchers twine, making ties 1 inch apart (you can use bamboo skewers to help hold the rolled belly together, while tying up with twine).
Place rolled roast into a roasting dish and refrigerate, uncovered, for about 6 hours.
Preheat oven to 325˚F.
In a small mixing bowl, combine sea salt and baking powder.
Pat porchetta dry with a paper towel and generously rub with salt and baking powder mixture.
Roast porchetta for about 1 hour and 45 minutes or until the internal temperature reaches 140˚F, basting every 30 minutes. Then continue to roast for an additional 1hr 30 minutes or until the meat, passed the skin, is soft and tender.
Increase oven temperature to 450˚F and roast for about 20 minutes, to get the skin extra crispy.
Remove from the oven and allow porchetta to rest for about 15 minutes (internal temperature should finish at 155-160˚F). Thinly slice with a serrated knife and serve.