Do-Ahead Scalloped Potato Casserole
2 1/2 tablespoons unsalted butter
1 med onion, minced
4 med garlic cloves, minced
1 ½ cups low sodium chicken broth or veg stock
1 ½ cups heavy cream
2 ½ teaspoons salt
½ teaspoon ground white pepper
3 bay leaves
3 1/2 pounds russet potatoes
½ pound sweet potato (can be made with all white potatoes)
Toppings: Cheese Topping:
1 1/2 cups shredded cheese. If using cheddar add 1 teaspoon dried thyme to the cream. If topping with Gruyere, Swiss, Emmenthal, or Parmesan add ¼ teaspoon nutmeg to the potatoes.
No Cheese Topping:
Add ¼ teaspoon nutmeg to the potatoes. Pour 1/3 cup heavy cream over the top and dot with 1 tablespoon butter
In a saucepan large enough to hold the potatoes, melt 2 tablespoons of the butter over medium high heat. Add the onions and sauté for 3 minutes or until softened and beginning to brown. Add the garlic and sauté for 30 seconds. Add the chicken stock, cream, salt, pepper, bay leaves and either the thyme or nutmeg and remove the pot from the heat.
Peel the white potatoes and hold covered in cold water until all are peeled. Slice the potatoes 1/8" thick (too thin or too thick won't cook properly). Immediately put the sliced white potatoes in the pot with the stock and cream or they will go grey. Continue until all the white potatoes are sliced. Bring the potatoes to a simmer, lower the heat to medium low, cover and simmer the potatoes for 10 minutes, gently turning them over. Peel and slice the sweet potatoes and add to the pot. Continue simmering for an additional 5-10 minutes or until the potatoes are just cooked or when a paring knife can be inserted easily in a potato slice.
Carefully pour the potatoes in the casserole and remove the bay leaves. Shake the pan and using a fork evenly distribute the potatoes. Press gently into an even layer.
To serve right away: Sprinkle the cheese or cream over the top and bake in the middle of a 400 degree preheated oven uncovered at 400 for 20-30 minutes or until the top is golden and the casserole is bubbling. Let cool for 10 minutes before serving.
To store and serve later: Let the casserole cool for 15 minutes. Cover with plastic wrap and poke vent holes in the plastic. Refrigerate for up to 2 days or freeze (wrap with plastic and then aluminum foil) for up to 1 month. If frozen thaw in the refrigerator for at least 24 hours before baking. Remove the wrapping and top with the cheese or cream. Cover the dish tightly with aluminum foil and bake in the middle of a 400 degree preheated oven for 30 or 40 minutes or until warm. Remove the aluminum foil and bake for an additional 30-40 minutes or until the top is golden and the casserole is bubbling. Let cool for 10 minutes before serving.
Note: the casserole can be run under the broiler to brown further.