2 tablespoons butter, room temperature
2 tablespoons finely chopped fresh dill, plus more for garnish
1 small garlic clove, minced
Coarse salt and ground pepper
8 ounces red new potatoes, scrubbed and thinly sliced
1 pound skinless cod fillet, cut into four equal pieces
8 ounces frozen uncooked medium shrimp (peeled and deveined), thawed
2 ears corn, quartered
1 lemon, thinly sliced
2 hard rolls, halved
Heat grill to medium. In a small bowl, combine butter, dill, and garlic; season with salt and pepper. Set aside.
Fold four 14-inch squares of heavy-duty aluminum foil in half, forming 4 rectangles. Assemble packets: On one half of each of four folded pieces of heavy-duty foil, dividing ingredients evenly, arrange potatoes in a single layer; top with cod, then shrimp. Place 2 pieces of corn on the side. Season with salt and pepper. Add a dollop of the butter mixtures and two lemon slices. Fold foil over ingredients, and crimp edges tightly to seal.
Place packets on grill, with potato layer on the bottom. Cook, rotating (but not flipping) packets occasionally, until fish is just cooked through and potatoes are tender, 12 to 14 minutes.
Remove from grill. Slit packets open, and transfer contents to serving bowls. Garnish with dill sprigs; serve with rolls.