Season and prepare the sole. Heat the oven to 350°F (180°C). On a cutting
board, cut the sole fillet in half crosswise. Season the flesh-side of the fillet with
salt, then stack the smaller half on top of the large half.

Create and fill the paper packets. Line a rimmed baking sheet with parchment paper, and place the stacked fillets in the center. Arrange the lemon slices evenly over the top of the fillet, then scatter the tomato halves, olives, capers, and parsley evenly over the fish. Drizzle everything lightly with olive oil.

Seal the paper packets. Brush the edge of the parchment paper lightly with the egg wash, then place another sheet of parchment paper over the fish so that it lines up with the first sheet. Starting at one corner, fold the edge of the sheets of paper up and over a few times to form a folded barrier, then continue moving along the edge and folding in the same way until the fish is fully encapsulated.

Bake the fish. Place the baking sheet in the oven, and bake until the fish is cooked through, about 25 to 30 minutes. Remove the baking sheet from the oven, and use scissors to carefully cut a slit in the top of the packet. Peel back the paper (be mindful of the hot steam that will escape). Using a flat metal spatula,
transfer the fillets to a plate. Spoon all of the aromatics and sauce left in the bag over the fish to serve.