2tablespoonsdark brown sugar(or light brown sugar)
1pinchred pepper flakes(or to taste)
2teaspoonsolive oil(or similar (Note 1))
Add the pork tenderloin to a large zipper-top bag. Add the soy sauce, vinegar, brown sugar, garlic, ginger, pepper, and pepper flakes.
Seal the bag, pressing out the air, and squish around to ensure the pork is coated with the marinade. Refrigerate for at least 4 hours or up to 8 hours (or overnight).
Preheat the oven to 375 degrees. Preheat a cast iron skillet over medium-high heat. Add the oil to the pan.
Add the tenderloin to the hot skillet. Transfer the marinade to a small saucepan and set aside.
Cook the pork for 2-3 minutes per side until brown. Transfer the skillet to the oven and bake for 15-25 minutes until the internal temperature reaches 145 degrees. (Note 2)
While the pork cooks, bring the marinade to a boil. Reduce to a low simmer to thicken the sauce.
When the pork is done, rest for three minutes before slicing.
Strain the marinade and pour over the sliced pork or serve on the side.
Oil is best to use because it has a higher smoke point than butter. Butter will burn which will lend a bitter, unpleasant flavor to the pork.
The cooking time will depend on the size and thickness of the pork tenderloin. Start checking the temperature after 10-12 minutes. Always use an instant-read thermometer to ensure the proper doneness of the pork.
Store leftovers for 4-5 days in the refrigerator in an airtight container.
Reheat in a skillet with a thin layer of chicken or vegetable broth. Cover the pan and heat slowly until warmed through. Alternatively, place the sliced pork in a baking dish with a thin layer of broth, cover with aluminum foil and heat at 325 degrees until warm.