Preheat oven to 400ºF.

Thickly butter a 9" cast iron skillet. Lay potato slices slightly overlapping in concentric circles, covering the bottom of the pan; repeat with another layer. Sprinkle with half the garlic and green onion, season with Creole seasoning. Dot with butter. Add another layer of potato, the remaining garlic and green onion, and season with Creole seasoning. Dot with butter. Top with remaining potatoes, butter, and Creole seasoning; cover with buttered layer of foil. Weight down with another (oven-proof) heavy pan; place over medium heat on the stove top and cook for 10 - 15 minutes, until the bottom browns. Take care not to burn.

Transfer to oven and bake until potatoes are soft, 30 - 45 minutes. Turn out upside down onto a platter or cutting board and serve at once, using a pizza cutter to slice.