1 large russet potato, scrubbed and sliced 1/8-inch thick
1 clove garlic, finely chopped
2 ounces baby spinach, well washed
2 medium shallots, thinly sliced
1 lemon, thinly sliced
2 6-ounce halibut fillets, about 1 1/2 inches thick
Coarse salt and freshly ground pepper
Preheat oven to 400 degrees. Using two 12-by-17-inch sheets parchment paper, fold each sheet in half crosswise.
Place 1 sheet of parchment flat on a work surface. Place half of the potatoes, garlic, spinach, shallots, and 2 lemon slices on one side of the crease; season with salt and pepper. Place halibut on top of lemon slices, and season with salt and pepper. Fold parchment over ingredients. Make small overlapping folds along the edge to seal.
Place packets on a baking sheet. Bake until packets have puffed, and fish is cooked through, about 18 minutes. Transfer packets to individual plates. Serve immediately, opening packets at the table. Garnish with any remaining lemon slices.