From these attempts we've identified several key steps that consistently gets good results, but first let's understand what this crispy, bubbly, crackly skin is all about. Essentially what this represents is a second degree burn of the pork skin. We have to have expose the skin to enough heat to burn through the thick layer of skin to get bubbly blisters without charring it. At the same time, this heat will render out fat and contract the skin, resulting in the desirable hardened and crackly and not rubbery texture. The second key step is to make the skin as dry as possible. Leaving the skin to dry overnight or 24 hrs in the fridge while the dry seasoning rub permeates on the belly side helps both in terms of crackly skin and flavor. Finally, scoring the skin helps render the fat, also helping to crispen the skin. However, there are also many ways to score the skin from diamonds to simple slits, to tiny pricks with nails. There is no one correct way, but we like to keep the skin intact so we use a small clean nail or large safety pin to prick the skin all over (some Asian markets sell meat tenderizers embedded with many nails).
A traditional porchetta is rubbed with a spice blend of garlic, rosemary, and fennel. But typically for our holiday parties there is always a dichotomy of traditional "American" vs. traditional "Vietnamese/Asian." So to appease everyone, we instead rubbed it with a spice rub highlighted by 5 spice powder. But feel free to substitute your spices and try our roasting method. We also brined the pork tenderloin, but this step is optional, especially if you are salt adverse.