Preheat your oven to 400°F. Slice the peeled potatoes into uniform ¼-inch rounds, using a mandolin or food processor for precision.

In a large mixing bowl, combine the sour cream, half and half, and French Onion Soup Mix, whisking until thoroughly blended. Add the sliced potatoes and half a cup of the shredded cheese, stirring until the potatoes are evenly coated.

Pour the mixture into a 2.5 to 3-quart baking dish, spreading it evenly. Cover the dish with a lid or aluminum foil.

Bake for 50 to 55 minutes at 400°F, checking for tenderness by piercing the potatoes with a fork.

Uncover the dish and scatter the remaining cheese evenly over the top.

Return to the oven and continue baking for an additional 10 to 15 minutes, or until the top is golden and bubbly.

Remove from the oven and allow the dish to rest for 10 minutes before serving.