Slightly Adapted from: food.com
3 lbs red potatoes or 3 lbs potatoes
5 tablespoons butter
6 tablespoons flour
2 1/4 cups heavy whipping cream
1 cup milk
2 teaspoons salt
2 cups swiss gruyere cheese, plus extra for topping
1. Preheat oven to 350°F.
2. Peel and slice potatoes about 1/8 inch thick. Boil in salted water until the start to become tender (just a few minutes). Continue to check on them. Do not fully cook them as they will continue to cook in the oven. Set aside.
3. In a large saucepan, melt butter over medium heat.
4. Add flour; stir while cooking, 1-2 minutes.
5. Whisk in cream. Add milk. Continue to cook until thickened.
6. Stir in swiss gruyere. Add potatoes to sauce and stir to mix evenly.
7. Pour into casserole dish. Sprinkle remaining cheese over top.
8. Bake casserole 45 minutes or until potatoes are tender and dish is bubbling and lightly brown on top. Let stand 5 minutes before serving.