Preheat oven to 420 degrees and cover a large baking pan with foil.
Chop and mash the garlic cloves with the sea salt to a chunky paste.
Whisk together the olive oil, mustard, lemon juice, fresh thyme, black pepper, and garlic mash/paste.
Place the meat on the foiled pan and proceed to spread the marinade all over the tenderloin(s) until every single inch is generously covered.
Tent the pan with a piece of aluminum foil on top. Tuck the top foil into the bottom foil, creating a "cartoccio" around the pork but making sure it stays loose (tentlike) at the top without touching the meat.
Bake for 25 minutes and check the temperature with a meat thermometer, making sure that it reads at least 150F.
Take off the top foil slowly and carefully. Make sure you wear oven mitts as the steam is very hot.
Pour all the juices and bits into a pan or a bowl. You can proceed to reduce them and make gravy, or you can simply reserve them to spoon over the roast right before serving.
Set your oven to broil, and bake the uncovered tenderloin(s) for 10 more minutes (5 minutes per side).
When the meat is a nice golden brown, take it out of the oven and leave it on a cutting board with a piece of foil loosely placed on top, sides left open. It needs to rest for at least 10 minutes to prevent the juices from running, leaving the pork too dry.
Transfer the roast to a serving platter. If you like what I did, you can garnish it with some of the ingredients, like lemon slices and sprigs of fresh herbs.
Slice into 1-inch pieces or thicker and serve with gravy on the side or spoon over the reserved juices.