Doesn't the traditional porchetta consist of the entire pig? I'm okay with substituting a cut of meat for kitchen finesse. I've done the Zuni Mock Porchetta, by Judy Rodgers, more times than I can count--it's so perfect that I've stopped experimenting.
Buy a 3-3 1/2 lb boneless pork shoulder TODAY, for this weekend. If you want more, buy two pork shoulder roasts--you want lots of crunchy golden outside bits to yummy scrummy inside bits.
Separate the seams. Salt it all over with 1/2 tsp salt per pound of meat. Stuff the seams with a mix of /capers/lemon zest/rosemary/sage/fennel seeds/black papper, roll it up again and tie it together. Let sit in your fridge for 1 to 3 days. THIS IS IMPORTANT. The presalting does wondrous things to the porchetta.
Roast at 350 with a bunch of root veggies, turning the roast so the veggies cook in the rendered fat. Add 1/3 c of chicken stock a couple hours in. Cook pork to 185 F--this will take 2 1/4 to 2 1/2 hours. Let it rest, tented with foil.
Skim fat off the pan, add vermouth and 1/3 C stock to make pan sauce.
Here is an online version of the recipe:Zuni Cafe Mock Porchetta/