Peel the potatoes and slice them very thin. Place in a bowl of cold water until ready to use.
Clean the fish and rinse under running water. Pat dry with a paper towel to remove excess moisture. Grease a baking dish with olive oil. Place the fish in the dish (photo 1). Grate lemon zest over the fish. Then slice this same lemon (photo 2) into wedges and place 1–2 wedges inside each fish (photo 3). Also place fresh parsley inside the fish (photo 4).
Add thinly sliced potatoes underneath the fish or arrange them all around. Cut a head of garlic (photo 5) crosswise and place it in the center of the dish. Grate a piece of stale bread over the fish or sprinkle with breadcrumbs. Add thinly sliced potatoes underneath the fish or arrange them all around (photo 6)
Add salt and pepper (I used peppercorns, crushed manually with a knife).Pour beer over the fish.Bake in a preheated oven at 180 °C (356 °F) for 20 minutes.Serve immediately.