Preheat the oven
Preheat your oven to 350°F (175°C).

Prepare the baking dish
Grease a 9×13-inch baking dish with butter or nonstick spray to prevent sticking.

Mix the sauce
In a large mixing bowl, combine the sour cream, melted butter, milk, and the French onion soup mix. Stir until fully incorporated into a creamy mixture.

Layer the potatoes
Arrange the thinly sliced potatoes evenly across the bottom of the greased baking dish.

Coat with sauce
Pour the sour cream mixture over the potatoes, using a spoon or spatula to spread it evenly and coat all the slices.

Season
Add salt and pepper to taste over the top.

Bake covered
Cover the dish tightly with aluminum foil and bake in the preheated oven for 45 minutes. This step helps the potatoes cook through and absorb the creamy flavors.

Add cheese & finish baking
After 45 minutes, remove the foil. Sprinkle the shredded cheddar cheese generously over the top. Return to the oven and bake uncovered for an additional 15 minutes, or until the cheese is melted, bubbly, and golden and the potatoes are fork-tender.

Serve hot
Let the dish rest for a few minutes before serving. Serve hot and enjoy the creamy, cheesy deliciousness!