1 (10.5 oz.) can cream of mushroom soup, 1/4 cup sharp cheddar cheese, grated 1/4 cup gruyere cheese, grated, 1/8 cup Parmesan cheese, grated, 5 white mushrooms, cleaned and sliced, 2 tablespoons minced garlic, 1 teaspoon ground thyme, 1 teaspoon sea salt, 1/2 teaspoon black pepper, 1 cup evaporated milk, 2 tablespoons self-rising flour, 2 tables butter, 5 cups Yukon gold potatoes, thinly sliced.
Preheat oven to 350 degrees. Get out a skillet, add the butter, melt; add the flour and 1 teaspoon of salt, stir with a whisk until the roux thickens, add 1 cup evaporated milk, continue to stir, make sure the roux stays blonde. Remove from the heat and set aside. Get out a bowl, add the soup, 1/2 of the cheeses, garlic, thyme, salt, and pepper, mix well. Add the soup mixture to the roux, bring to a boil, reduce to a simmer cook for about 2-3 minutes, remove from the heat, set aside. Get out a large cast iron skillet lightly grease the skillet with butter. Add the potatoes to the skillet, pour the roux on top mix together. Bake for about an hour, check the potatoes they should be a little softer than fork tender if they are, evenly add the remaining cheeses on top return to the oven and continue to bake until the cheese melts and is bubbly.