4 (6-ounce) skin-on salmon fillets
2 tablespoons extra-virgin olive oil
Kosher salt and pepper
1 pound asparagus, tough stems trimmed, stalks sliced 1/4-inch-thick on a slight bias (leave tips whole)
4 tablespoons unsalted butter
1 tablespoon fresh lemon juice, plus wedges for serving
2 tablespoons drained capers
1/2 cup thawed frozen peas
1/4 cup coarsely chopped parsley, plus more for garnish
Heat oven to 450 degrees. Rub salmon all over with 1 tablespoon oil and season with salt and pepper. Arrange skin side-down on a rimmed baking sheet and roast until medium, 8 to 10 minutes.
While the salmon roasts, prepare the asparagus: In a large skillet, heat the remaining 1 tablespoon oil over medium-high. Add asparagus, season with salt and pepper and cook, stirring occasionally, until crisp-tender, about 3 minutes. Transfer asparagus to a plate.
Reduce heat to medium and add butter to skillet. Cook, stirring, until foam subsides and butter is deep golden brown, 2 to 3 minutes. (Be careful not to burn). Turn off heat and stir in lemon juice, capers, peas, parsley and cooked asparagus. Season with salt and pepper.
Divide vegetables among plates. Top with salmon and spoon over any remaining pan sauce. Garnish with parsley and serve with lemon wedges.