Preheat the oven to 425F each.
Cut parchment paper into large squares and place the fish in the center. Add one fillet per square.
Sprinkle with salt and pepper and arrange the leeks, herbs, and garlic cloves over the fish.
Wrap the fish by folding the parchment paper over and pleating the edges so it stays closed. Before you “seal” the paper, add the white wine and dot it with the butter.
Bake until the paper is browned and puffed, about 15 minutes. Unwrap and ensure the fish is firm and opaque throughout or a thermometer registers 125F to 130F. Serve immediately.