Pat the turkey tenderloins thoroughly dry on all sides with paper towels. In a small bowl, mix garlic powder, onion powder, smoked paprika, sea salt, and black pepper. Rub the turkey all over with the seasoning blend. Let rest at room temperature for 10 minutes while preheating oven to 400°F (204°C).

Heat 1.5 tablespoons olive oil in a heavy 12-inch oven-safe cast iron skillet over medium-high heat until shimmering. Add the turkey tenderloins and sear undisturbed for 3 to 4 minutes per side until deeply golden and caramelized on all sides.

Reduce heat to medium. Drop the butter cubes, minced garlic, rosemary sprigs, thyme, and sage directly into the hot skillet. As the butter melts and foams vigorously, tilt the skillet slightly and use a large spoon to baste the frothing garlic herb butter continuously over the tenderloins for 1 to 2 minutes.

Pour the chicken broth around the turkey tenderloins into the skillet. Transfer the cast iron skillet directly into the preheated 400°F oven. Roast for 15 to 18 minutes, or until an instant-read meat thermometer inserted into the thickest center registers 160°F (71°C). Transfer turkey to a cutting board, tent loosely with foil, and let rest for 10 minutes to lock in juices (carryover cooking will bring it to the perfect safe 165°F). Carve into thick slices and spoon warm skillet garlic herb butter sauce over top.