1. Before you start cooking your tenderloin, let it sit on the counter at least 15 minutes before you place it in a hot pan. Pat the pork tenderloin down with a paper towel before you season it. This will allow it to cook evenly and get a nice gold brown crust on your meat.
2. Move oven rack to the upper third part of your oven (enough room for your tenderloin to be close to the top without touching the coils. Try to have an inch or two between your tenderloin and the top of the oven. Preheat the oven to 400 degrees.
3. Generously sprinkle salt, pepper, chopped rosemary, and Italian seasoning over both sides of pork tenderloin. Use butcher twine to tie loin together if needed.
4. In a large oven proof skillet, heat oil. Add pork to skillet, fat side down.
5. Cook over moderately high heat until golden brown, 4 minutes. Brown pork on the remaining sides, then turn it fat side up. Add garlic to the side of pork and cook stirring, letting garlic soften but not brown.
6. Add the orange juice, chicken stock, and bring to a boil.
7. As soon as you see bubbles along the side of the pan, transfer the skillet to the upper shelf of the oven and roast the pork for about 35 minutes, or until thermometer reads 145 degrees.
8. Transfer to cutting board and let res, then slice.
9. Place skillet on stove top and turn to medium-high heat until reduced to 1/2 cup, about 7 minutes. Sever sauce alongside sliced pork.