Preheat oven to 400°F.
In a small bowl, combine kosher salt, sage, garlic powder, onion, powder, and ground black pepper. Set aside.
Trim the pork tenderloin of any excess fat and silverskin. Pat the pork dry, rub with 1 tablespoon of olive oil; rub seasoning mixture on all sides of the meat.
Heat remaining 2 tablespoons of olive oil in a large skillet over medium heat. When the oil shimmers, add pork; cook until browned on all sides, about 4-5 minutes total. Transfer to a foil-lined rimmed baking sheet.
Place maple syrup, butter, mustard, garlic cloves, rosemary, and vinegar in the same skillet that you used to brown the meat. Bring to a boil, stirring or whisking to loosen the browned bits from the bottom of the pan. Cook and stir until slightly thickened, 1-2 minutes. Remove from the heat. Discard rosemary sprigs and garlic cloves.
Brush about half of the glaze over the pork.
Transfer the pork to the oven, uncovered, and bake until a thermometer inserted in the thickest portion of the meat registers 140°F - 145°F, about 10-13 minutes. Baste with the remaining glaze about halfway through the cooking time. For a crisp, charred exterior, place the pork under the broiler for the final 1-2 minutes.
Let the pork rest at room temperature for at least 5-10 minutes before slicing and serving.