What You Need
Season salmon with salt and pepper. Heat 1 tablespoon of the oil in a 4.5 QT Hexclad deep sauté pan over medium-high heat. Add salmon skin side down and cook, until skin is golden and crisp, 5 to 7 minutes. Flip salmon and continue to cook until flesh side is light golden and salmon is medium-rare, 1 to 2 more minutes. Remove salmon to a plate.
Drain oil from sauté pan and discard. Return sauté pan to medium-high heat and add asparagus and the remaining tablespoon of oil and cook, tossing several times, until asparagus is lightly charred in places and crisp tender, about 5 minutes. Remove asparagus to a plate.
In the same sauté pan over medium heat, add 2 tablespoons of the butter, garlic, and pepper flakes and cook, stirring, until light golden, about 3 seconds. Pour in broth and bring to a simmer. Add remaining 6 tablespoons butter, lemon zest and juice, and sriracha and cook, stirring constantly, until butter is melted and combined.
Remove from heat and stir parsley into butter sauce. Season with salt and pepper. Return salmon and asparagus to pan and spoon sauce over both. Sprinkle with more parsley and serve.