Ingredients
2 skinless flounder or sole fillets (each 5 to 6 ounces and about 1/2 inch thick)
Kosher salt and freshly ground pepper
2 ounces shiitake mushrooms, stemmed and thinly sliced (3/4 cup)
6 ounces thin asparagus, trimmed, lower halves peeled (if using thicker asparagus, halve lengthwise)
1/2 small red onion, thinly sliced (1/2 cup)
1/4 cup dry white wine, such as Sauvignon Blanc
2 tablespoons unsalted butter, cut into small cubes
Preparation
Preheat oven to 450 degrees. Fold two 13-by-19-inch sheets of parchment in half from short ends to create a crease in each; unfold. Place each fillet to one side of a sheet, abuttingcrease; generously season with salt and pepper. Scatter mushrooms, asparagus, and onion evenly around fillets. Drizzle each fillet with 2 tablespoons wine. Scatter butter evenly over fish and vegetables; season with salt and pepper.
Fold each sheet over fish and vegetables. Starting on one side, roll bottom side of parchmentup and over top side to seal; continue working around until pouch is sealed in a half-moonshape. Transfer both pouches to a rimmed baking sheet.
Steam-roast until parchment puffs and darkens slightly and fish is just cooked through, 10 to12 minutes. Carefully rip open pouches (scalding steam will be released) and serve.
