Begin by shredding the lion's mane by hand into small pieces and add them to a medium-sized pot along with a pinch of sea salt and about 2 tablespoons of water. Cover and allow the mushrooms to sweat over low heat for 5-10 minutes, stirring occasionally.
Allow the mushrooms to cool, then squeeze the excess water out of them. Place the mushrooms in a large bowl.
Add mayonnaise, egg, lemon juice, Worcestershire sauce, dijon mustard, celery, serrano, parsley, Old Bay, and Panko breadcrumbs to the mushrooms. Mix thoroughly.
Form mixture (coating your hands in flour will make this easier). Cover each side flour to absorb the moisture, then set on a flour-coated or parchment paper lined plate.
Fry the cakes in a pan or skillet over medium heat for about 3-4 minutes on each side or until golden brown. Set them on a paper towel to drain the excess oil.