- 1 1/2 pounds slender asparagus spears, trimmed to 7-inch lengths
- 2 garlic cloves, minced
- 1 teaspoon salt
- 2 tablespoons (1/4 stick) butter
- 1 tablespoon plus 6 teaspoons olive oil
- 1/3 cup fresh lemon juice
- 1 1/2 teaspoons grated lemon peel
- 1/2 teaspoon ground black pepper
- 6 6-ounce cod fillets, pinbones removed
- 6 ounces paper-thin prosciutto slices, halved lengthwise
- Cook asparagus in large pot of boiling salted water until crisp-tender, about 3 minutes. Drain. Transfer to bowl of ice water to cool. Drain well.
- Mash garlic and 1 teaspoon salt to paste in small bowl. Melt butter with 1 tablespoon oil in small nonstick skillet over medium heat. Add garlic paste; stir until pale golden, about 1 minute. Stir in lemon juice, peel, and 1/2 teaspoon black pepper. Remove from heat.
- Preheat oven to 500°F. Cut out six 12-inch squares of parchment paper. Place 1 parchment square on work surface. Drizzle 1 teaspoon oil over parchment. Place 1 cod fillet in center of parchment. Spoon 1/6 of garlic-lemon mixture over fish. Cover with 1/6 of asparagus spears. Arrange 1/6 of prosciutto slices over. Fold 2 opposite sides of parchment in over fish and vegetables, then fold in remaining 2 sides, enclosing completely. Fasten parchment edges together with paper clips to seal packet. Place on large rimmed baking sheet. Repeat procedure with remaining parchment, oil, fish, garlic-lemon mixture, asparagus, and prosciutto. (Can be prepared 6 hours ahead. Refrigerate.)
- Bake fish until just opaque in center (parchment will turn golden brown), about 12 minutes. Transfer 1 parchment packet to each of 6 plates. Open parchment packets and serve.