Lay pork belly out skin side down. Place pork loin in the center of the pork belly and roll up to form a roast, making sure the pork belly evenly meets to totally enclose the roast. Trim any excess meat if necessary. Unroll and reserve for assembly.
Combine parsley, fennel fronds, garlic, sage, fennel seed, crushed red pepper, rosemary, and zests in a bowl. Moisten with olive oil to form a pesto like paste. Set aside.
Lay the pork belly out skin side up. Using a sharp paring knife or Jaccarding tool, prick the skin all over. Flip belly skin side down. Season generously with salt and evenly spread the spice and herb mixture all over.
Season the pork loin generously with salt and lay down middle of belly. Roll belly around loin and tie crosswise with kitchen twine at 1” intervals, beginning in the middle, then the ends, and fi nally the spaces in between.
Transfer the roast to a hotel pan lined with a roasting rack. Refrigerate for 1-2 days, uncovered, to allow the skin to dry out.
Remove the roast from the cooler and season with salt and pepper. Place in a 450°F convection oven and cook for 30-45 minutes or until the skin begins to blister and brown.
Drop the temperature to 300°F and continue cooking to an internal temperature of 145°F, about 1½ - 2 hours, depending on your equipment. Note: While cooking, monitor the browning and crisping progress of the skin. The goal is a deep amber brown color and crisp texture. Adjust temperature and oven placement accordingly. Basting with pan drippings will also accentuate browning.
Remove porchetta from oven and rest at least 20 minutes before carving. Serve simply with roasted fingerling potatoes and seasonal vegetables dressed with olive oil and sea salt.