How to Make It
In a medium saucepan, heat the vegetable oil. Add the corn, cover and shake over high heat until the kernels have popped. Add the the water, bonito flakes, chiles, rosemary, thyme and allspice and bring to a boil. Remove the saucepan from the heat, cover and let stand for 15 minutes. Strain the broth into a bowl and add the soy sauce and yuzu juice.
Light a grill. For each papillote, layer two 14-inch sheets of heavy-duty aluminum foil on a work surface. Fold up the sides of the foil to hold the broth. Divide the shiitake, shallots and ginger among the foil sheets. Season the fish with salt and pepper and set the fillets on the vegetables. Pour about 1 cup of popcorn broth over each fillet. Seal the packets, crimping tightly.
Grill the packets over high heat until the broth bubbles vigorously, about 10 minutes. Carefully open each packet. Transfer the fish to shallow bowls and drizzle with olive oil. Spoon the vegetables and broth over the fish and serve.