although I don't make it as often as I'd like to.
The sandwich filling is mushrooms, sauteed in butter and seasoned with nutmeg. Add a slice of Swiss or Gruyere cheese, Dip one side of your bread of choice in eggs and milk or (what I do) a loose pancake batter,set it gooey side down on the griddle, pile on the mushrooms, pop on the cheese, and cover with the second slice of bread, gooey side up.
I make it easier by using a domed lid over the griddle That partially cooks the top slice, melts the cheese, and sort of glues the whole business together. It should take about 5 minutes. Remove the dome and look and if the bottom slice looks dry and the cheese has melted, flip the sandwich over to brown the other side. Don't use the dome this time, you want the first side to stay crunchy.
This is a super cheap but super fancy take on mushrooms on toast. It can be held in a warm oven while brunch guests sip their Bloody Marys and other hair of the dog drinks.