Mushroom Gravy Scalloped Potatoes

Mushroom Gravy Scalloped Potatoes for the potatoes: 3 pounds Yukon Gold or Russet Potatoes , peeled and sliced thin 2 cups shredded Cheese , divided Optional- 1 small onion , sliced thin for the mushroom gravy 1/2 cup butter , divided 16 ounces mushrooms , sliced 2 cloves garlic , minced 1/3 cup flour 1 cup broth (beef, chicken or vegetable) 2 cups milk salt to taste black pepper to taste Preheat oven to 375°F. Butter an 9”x13” baking dish. Set aside. Make the gravy: In saucepan, melt half of butter (1/4 cup) over medium-high heat. Add garlic, cook until softened and then add mushrooms and cook until mushrooms are golden brown and excess mushroom liquid evaporates, about 5-10 minutes. Add remaining butter and cook until melted. Stir in the flour, cooking and stirring to remove lumps. Add about 1/2 cup of stock, whisking until incorporated. Pour in the remaining broth and milk. Whisk until well combined. Season with salt and pepper, to taste (the saltiness and flavors will concentrate some when it reduces down). Reduce heat to medium, stirring often, simmer until slightly thickened, about 15-20 minutes. Check for seasoning and salt again if needed. Remove from heat and set aside. Layer 1/2 of the potatoes in the prepared baking dish, making sure to separate slices. Top with half of the gravy. Layer half of the sliced onions. Layer about 1/2 of the cheese over the potatoes. Top with the remaining potatoes (making sure to separate slices). Top with remaining gravy, onions and cheese. Cover the pan with aluminum foil. Bake for 1 hour, the remove foil and bake uncovered for about 25-30 minutes or until top is golden and potatoes are cooked through. Serve warm. Note: If you're using a smaller and taller baking dish than a 9"x13", it might take a little longer to cook because the volume of potatoes are higher and thicker.