A few tablespoons of unsalted butteror cooking oil
Inspect the Gyromitra for bugs, debris, and dirt. Clean the mushroom diligently, swishing around in a bowl of cool water as needed to loosen any dirt. Cut it in half if small or quarter them if large and inspect diligently for bugs and debris.
Open all the windows in your kitchen, and use a kitchen hood fan if available, or use a box fan to blow air out of the kitchen if you're cooking Gyromitra esculenta or others with higher amounts of gyromitrin. (See safety note)
Bring a pot of water to a rolling boil, add the gyromitra, put a lid on the pot, bring it back to a rolling boil and cook for 10-15 minutes, depending on how many you're cooking, or until they're completely cooked and wilted.
Remove the Gyromitra. Discard the water. Put the Gyromitra between a few sheets of paper towels and press to get out as much water as possible. Season both sides of the mushrooms with salt.
Heat the butter in a skillet, like cast iron, and cook the mushroom on medium low heat about, flipping once, for about 5 minutes on each side, or until the mushroom is deeply caramelized and browned, then drain for a moment or two on a paper towel to shed fat, and eat. Sprinkle some extra salt as you eat if you think it needs it.
Safety notesDon't serve Gyromitra to people who don't know or understand what they are. Some Gyromitra must be par-boiled before cooking, especially Gyromitra esculentaVentilationI recommend using ventilation, fans, or a hood vent while par-boiling, but it's in the interest of being overly cautious, and some species are fine cooked in your kitchen, like Gyromitra korfii, brunnea, and caroliniana, for example. Gyromitra esculenta must be par boiled, as well as some others. Some species are reputed to not need par boiling, but you're on your own to experiment there.