Preheat your oven to 400°F (200°C).

In a large skillet over medium heat, add 1 tablespoon of olive oil. Once hot, add the pearl onions and sauté until they are golden brown and tender, about 10 minutes. Season with salt and pepper. Remove from heat and set aside.

In a small bowl, combine the rosemary, thyme, garlic powder, onion powder, smoked paprika, salt, and pepper. Rub this mixture all over the sirloin steak.

In the same skillet, heat the remaining tablespoon of olive oil over medium-high heat. Add the seasoned sirloin steak and sear for 4-5 minutes on each side until a nice crust forms.

Transfer the seared steak to a baking dish and surround it with the toasted pearl onions. Place in the preheated oven and roast for about 15-20 minutes for medium-rare, or until your desired doneness is reached. Use a meat thermometer for accuracy (130°F for medium-rare).

While the steak is roasting, prepare the mustard-garlic confit butter. In a bowl, mix together the softened butter, Dijon mustard, minced garlic, parsley, and lemon juice until well combined. Set aside.

Once the steak is done, remove it from the oven and let it rest for 10 minutes. This allows the juices to redistribute.

Slice the sirloin and serve it topped with the toasted pearl onions and a generous dollop of the mustard-garlic confit butter.