The way I remember this, it was Jeanne’s wedding, and a neighbor, Olga, was catering maybe the rehearsal dinner? And Grandpa asked me to see if I could get Olga to give me the recipe for the mushroom casserole. It’s great served with beef! She generously gave it to me, and I’ve been making it every Christmas since then with our Prime Rib.
Steam the mushrooms and onions to release their water and evaporate most of it (about 10-15 min). Then add in the butter to melt. When it does, stir in the flour to make a roux. Cook stirring for a few minutes over low heat. Season with salt and pepper. Continue to cook uncovered until the mixture thickens. Add the Worcestershire sauce. Stir in the chopped parsley, saving some for garnish at the end.
Pour mixture into a buttered dish, and sprinkle the panko or bread crumbs on the top. Sprinkle the nutmeg on the bread crumbs. Bake at 350 degrees for about 30 minutes until the bread crumbs are lightly browned.
Garnish with more parsley and serve with your meat dish. Doesn’t have to be beef, but for us, it usually is.