1. 1. Preheat and Prepare Your Pan: Begin by preheating your oven to 400 F (200 C). Line a large baking sheet with parchment paper for easy cleanup. This prevents sticking and makes transferring the cooked meal a breeze.

2. 2. Prepare the Asparagus: On one side of the prepared baking sheet, spread out the trimmed asparagus in a single layer. Drizzle with a tablespoon of olive oil, a pinch of salt, and pepper, tossing gently to coat.

3. 3. Season the Salmon: Pat the salmon fillets dry with paper towels. This helps achieve a nice sear and prevents steaming. Place the salmon fillets on the other side of the baking sheet, leaving some space between them and the asparagus.

4. 4. Create the Garlic Butter Sauce: In a small bowl, combine the melted butter, minced garlic, chopped fresh rosemary, fresh lemon juice, salt, and black pepper. Stir everything together until well combined. The sauce should be fragrant and slightly emulsified.

5. 5. Coat the Salmon and Asparagus: Spoon or brush the garlic butter mixture evenly over the salmon fillets. Ensure each fillet is well coated. You can also drizzle any remaining sauce over the asparagus for extra flavor.

6. 6. Bake Until Done: Transfer the baking sheet to the preheated oven. Bake for 15-20 minutes, or until the salmon is cooked through and flakes easily with a fork, and the asparagus is tender-crisp. The exact cooking time will depend on the thickness of your salmon fillets.

7. 7. Serve Immediately: Once cooked, remove the baking sheet from the oven. Garnish with fresh lemon wedges and serve hot. The salmon should be moist and flaky, and the asparagus vibrant green and tender.