Perfect Sirloin Tip Roast

Bahan-bahan (8 porsi)

• 1 sirloin tip roast (4-5 pounds)
• 2 tablespoons olive oil
• 1 teaspoon garlic powder
• 1 teaspoon black pepper
• 2 teaspoons kosher salt (more or less to taste)
• 1 teaspoon dried rosemary
• 1 onion