Preheat and prep: Heat the oven to 400°F (200°C). Pat the pork tenderloins dry with paper towels.
Season all over with salt and pepper.
Sear the pork: Heat a large oven-safe skillet over medium-high. Add 1–2 tablespoons oil. Sear the pork on all sides until deeply browned, about 6–8 minutes total.
Roast to finish: Transfer the skillet to the oven.
Roast until the thickest part reaches 140–145°F on an instant-read thermometer, about 12–18 minutes depending on size.
Rest the meat: Move the pork to a cutting board and tent loosely with foil. Let it rest 8–10 minutes to keep it juicy.
Start the sauce base: Return the skillet to the stove over medium heat. If the pan is dry, add a small splash of oil.
Sauté the shallot for 1–2 minutes until soft, then stir in garlic for 30 seconds.
Build the cranberry sauce: Add cranberries, broth, orange juice, honey or brown sugar, Dijon, thyme, and cinnamon. Scrape up the browned bits on the bottom of the pan.
Simmer and thicken: Cook 5–8 minutes, stirring now and then, until the cranberries burst and the sauce reduces slightly. If it looks too thick, splash in more broth.
Finish with brightness: Off the heat, stir in balsamic vinegar and the butter until glossy.
Taste and adjust salt, pepper, or sweetness as needed.
Slice and serve: Slice the rested pork into 1/2-inch medallions. Spoon the cranberry sauce over the top and garnish with herbs.