Trim the silver skin from the pork tenderloin and season with kosher salt, fresh ground pepper, garlic powder, onion powder, dried thyme, paprika, and poultry seasoning. Rest for 45 minutes.

In a large skillet, heat olive oil and butter over medium-low heat. Add thinly sliced sweet onions and cook for about 45 minutes until golden brown.

While onions caramelize, whisk together maple syrup, grainy mustard, minced garlic, balsamic vinegar, Worcestershire sauce, and a pinch of salt in a small bowl.

Heat remaining olive oil in a separate skillet over high heat. Sear the pork tenderloin on all sides for 4 to 6 minutes until golden brown.

Preheat oven to 400°F (200°C). Place seared pork on caramelized onions, drizzle glaze over tenderloin, and roast for 15 to 20 minutes or until internal temperature reaches 145°F (63°C).

Remove from oven and let the pork rest for 10 to 15 minutes. Slice and serve over caramelized onions with remaining glaze.