I made Porchetta the other day for my husbands birthday dinner. It turned out really well and I have just come across skinnymixers twice cooked pork roast. I am going to give it a try in the Thermomix. The Berkshire pork belly that I cooked was around 6 pounds so it wouldn't have fit in the Thermomix anyway but generally I don't cook for so many people.
You need to score the pork skin with a razor blade, super sharp knife etc. Don't cut into the meat but make sure you have cut through the skin. This helps the fat render.
We bought the Berkshire pork belly and put a salt, garlic, pepper and preserved lemon rub on the belly. We then rolled it up and salted it again with the rub and let it sit overnight in the fridge. We then slow baked it on a rack at 300F for about 2 hours. I then broiled it until crispy. Keep your eyes on it as it will burn quickly.