Potatoes Dauphinoise- Bomb Cheesey Baked Potatoes!

["preheat oven to 350F", "peel potatoes , cut into thin slices (1/8"" thick)", "combine and whisk milk and cream of mushroom in sauce pan over medium low heat", "melt 2 tablespoons of the butter in a seperate pan.", "then add onions , cook 2 minutes", "add sliced mushrooms to the pan with the onions.", "toss well so that the mushrooms are coated in butter all around.", "cook until tender and onions are translucent.", "meanwhile, in a mixing bowl whisk egg yolk together", "gradually whisk the cream of mushroom mix into the egg yolk.", "whisk slow and thuroughly", "now, with the remaining tablespoon of butter, grease a 2"" deep baking dish.", "add a layer of potatoe slices to the dish", "pour a portion of the cream of mushroom accross potatoes", "lightly sprinkly salt, pepper, nutmeg on potatoes", "disperse a portion of onions/mushrooms on top", "sprinkle cheese on top.", "repeat layers(3-4)", "bake 50-60 minutes.", "let cool 5-10 minutes and serve"]