4 tablespoons unsalted butter, at room temperature
Zest and juice of half a lemon
½ teaspoon dried herbes de provence
2-3 garlic cloves, minced
Pinch of red pepper flakes
Kosher salt and freshly ground black pepper
1 pound asparagus, woody ends removed
4 lemon slices, plus more for serving
4 (6-8 ounce) skinless white fish filets, about 1-inch thick
4 tablespoons dry white wine
Heat oven to 450º. Cut four pieces of foil, each about 10×14 inches. In a small bowl, use a fork to combine the butter, lemon zest and juice, herbes de provence, garlic, red pepper flakes and salt and pepper, to taste. Set aside.
Divide the asparagus evenly among the sheets of foil, sprinkle lightly with salt and pepper, top with a lemon slice and set aside. Pat the fish dry and season with salt and pepper. Spread 1 tablespoon of butter onto each fish, then carefully transfer to the foil packets. Pour 1 tablespoon of wine over each. Wrap and seal the packets, then place on a baking sheet.
Bake until the fish is just cooked through and the asparagus is crisp-tender, 15-20 minutes. Open the packets carefully. Serve the fish and asparagus with the accumulated juices in the packet and extra lemon, if desired.