Begin preparation 24 hours in advance.
In a food processor, combine ingredients for salt rub, pulsing until all ingredients are evenly distributed, remove to bowl.
Once again in the food processor, combine ingredients for herb rub, pulsing until combined.
Remove any bone from your pork shoulder. Once bone is removed, butterfly the pork shoulder. (See link below for deboning & butterflying pork shoulder)
Spread out the pork (skin side up), score the skin in a crosshatch pattern (making shallow cuts on the skin).
Once pork has been scored, spread out skin side down, spread the herb rub evenly on the inside of the meat, as well as two teaspoons of the salt rub.
Tightly roll meat so skin is covering the majority of the meat. Try to avoid having any skin wrapped inside the roast, as it won't crisp up, and that portion of skin will be unpalatable as a result.
Tightly wrap porchetta with cooking string.
Rub the rest of the salt mixture into the skin of the pork shoulder.
Place porchetta on a plate with paper towel, leaving in the refrigerator uncovered for 24 hours.
Heat oven to 275F
In the middle of the oven, place porchetta on a rack in a roasting pan. If you don't have a roasting pan, place the porchetta directly on your oven rack, with a dish large enough to catch all the dripping on the rack below.
Roast pork for about 2 hours or until internal temperature reaches 160F. My roast (3.5 lbs) cooked for about 30 minutes per pound, if you have a larger roast, prepare for a longer cook time.
Once pork has reached 150F, increase oven heat to 450F, roasting until the pig skin turns into golden brown, puffy crackling, and internal temperature is at least 160F. Keep a close eye on your porchetta in this final step, you don't want to burn the skin!
Depending on your oven you may need to rotate the porchetta to evenly cook the crackling. The top of my skin puffed up fairly quickly, so I rotated it to one side and cooked for a while, then rotated to the other side until evenly cooked.
Once cooked, remove from oven and allow to rest for at least 20 minutes before serving.
Slice porchetta and serve with salsa verde.
Prepare the salsa verde while porchetta is cooking.
To toast fennel and coriander, place in a dry pan on medium heat, cooking until it becomes fragrant, and lightly browned (about five minutes). Grind in food processor or with a mortar & pestle.
Combine all the ingredients for salsa verde in a food processor, processing until an even mixture is formed.