Preheat oven to 250 degrees F
Begin by making the sauce. To do that use a pan that can go into the oven. It doesn’t have to be a sauce pan but something that can fit the sauce and meat with a cover.
Add your olive oil to a heated pan over medium heat. Add the onion and salt. Let cook for 1 minute. Then add in jalapeno pepper and garlic. Let cook for 1-2 minutes. Add in both cans of sauce and the seasonings. Reduce to a simmer and cover.
Boil a medium pot of water and add a teaspoon of salt. Add the swiss chard for just 1-2 minutes then strain. When it cools using your hands and give a good squeeze to let all of the water out. Put on a cutting board and give it a rough chop and add it a bowl.
To the bowl add the shallot, garlic and seasonings. Mix together.
On a plastic board butterfly the tenderloin. Using a mallet pound the meat until there is an even layer of 1/2 inch thick. Season both sides with salt and pepper.
Take the swiss chard mixture and make an even layer to one side of the tenderloin. Fold to clover the filling and take the twine and secure.
Take a large sauté pan and put over medium/high heat – Add a tablespoon of olive oil and sear all sides (about 3 minutes on each side).
Take out of the pan and place into the sauce mixture. Let simmer for 10 minutes then put in the oven for at least 3 hours.
When the meat is done it will be fork tender. Melt in your mouth Pork!
This would be great with roasted butternut squash or other seasonal vegetables.