Note: Use a cast iron skillet to sear/roast the meat if possible. This provides a great sear and is also oven safe. If your skillet is not oven safe, be sure to transfer the pork/pan sauce to an oven safe baking dish before roasting.
Preheat oven to 400° F.
Combine the seasonings in a small bowl. Pat the pork completely dry and rub the seasoning over the surface.
Heat olive oil in a large, wide skillet over medium-high heat. (Preferably cast iron.) Make sure it's sufficiently heated before adding the pork so that it sizzles right when the meat hits the skillet.
Add the pork and sear on all sides until golden, 6 minutes total.
Transfer to a plate and set aside. Turn heat off and let the skillet cool for a minute.
Add the wine and set the heat to medium. Add the butter, beef broth, smashed garlic cloves, and sliced onions to the skillet and set the heat to medium. Use a silicone spatula to “clean” the skillet. Bring to a boil and boil/reduce for 5 minutes. Remove from heat and let it cool for 2 minutes.
Add the pork to the skillet along with any juices from the plate. Roast uncovered for 15 minutes. (Thinner tenderloins will need 13 minutes, thicker will need 15.)
Remove from the oven and spoon the pan sauce over the pork.
Let it rest in the skillet for 10 full minutes, (set a timer). This is key to lock in the juices and to let the pork continue to rise up to temperature.
After resting, ensure the internal temperature of the thickest part of the pork is 145° F. When sliced, the pork should be light pink and juicy. (If needed, return the pork to the (still hot) oven to rise a few more degrees in temp. I never find this necessary but it may be for thicker cuts.)
Cut into ¾-inch slices and drizzle with pan sauce prior to serving. (See notes for instructions on how to make gravy with the pan sauce!)
Serving suggestion: Mashed potatoes and brown gravy.