Preheat your oven to 350°F (175°C). Lightly grease a 9x13-inch baking dish.

Peel and cube the potatoes into 1-inch pieces. Boil in salted water for 8-10 minutes until fork-tender, then drain.

In a mixing bowl, combine sour cream, cream of mushroom soup, and French onion soup mix. Stir in melted butter. Fold in the drained pineapple and shredded cheese until coated.

Add parboiled potatoes to the sauce mixture and coat evenly. Transfer to the prepared baking dish.

Sprinkle additional cheese and optional breadcrumbs on top. Bake uncovered for 40-45 minutes until golden brown and bubbly.

Let the casserole cool slightly before serving, about 5 minutes.