Nestle the belly into a roasting pan or other oven-safe vessel that holds it snugly. Mix together the salt and sugar in a small bowl and rub the mix all over the meat; discard any excess salt-and-sugar mixture. Cover the container with plastic wrap and put it into the fridge for at least 6 hours, but no longer than 24.
Heat the oven to 450F
Discard any liquid that accumulated in the container. Put the belly in the oven, fat side up, and cook for 1 hour, basting it with the rendered fat at the halfway point, until it’s an appetizing golden brown.
Turn the temperature down to 250F and cook for another 1 hour to 1 hour 15 minutes, until the belly is tender. It shouldn’t be falling apart, but it should have a down pillow-like yield to a firm finger poke. Remove the pan from the oven and transfer the belly to a plate. Decant the fat and the meat juices from the pan and reserve. Allow the belly to cool slightly.
When it’s cool enough to handle, wrap the belly in plastic wrap or aluminum foil and put it in the fridge until it’s thoroughly chilled and firm. (You can skip this step if you’re pressed for time but the only way to get neat, nice-looking slices is to chill the belly thoroughly before slicing it)
Cut the pork belly into 1/2 inch thick slices that are about 2 inches long. Warm them for serving in a pan over medium heat, just for a minute or two, until they are jiggly soft and heated through. Use at once.