Preheat your oven to 350°F (175°C).

Peel and slice the russet potatoes into thin, uniform rounds, about an eighth of an inch thick.

In a large mixing bowl, combine sour cream, shredded cheddar cheese, grated Parmesan cheese, melted butter, and chopped green onions. Season with salt and pepper to taste. Stir well until thoroughly blended.

Grease a baking dish lightly with butter. Start with half of the potato slices, then pour half of your creamy filling over the first layer, coating each slice. Repeat with the remaining slices and filling.

Sprinkle breadcrumbs evenly over the top layer. Optionally, add more cheese for extra flavor.

Cover the dish with aluminum foil and bake for 30 minutes.

Remove the foil and continue baking for an additional 15 to 20 minutes, or until the top is golden brown and the edges are bubbly.

Let the dish cool for a few minutes before serving.