- 1/2 head small green cabbage (from a 1 1/2- to 2-pound whole cabbage), halved again and cored
- 2 pounds large boiling potatoes, preferably Yukon Gold
- 1/2 cup chopped scallions
- 5 tablespoons unsalted butter, divided
- 1 large egg, lightly beaten
- Special equipment: a 9-inch pie plate, potato masher
- Steam cabbage in a steamer set over boiling water, covered, until just tender, 15 to 25 minutes. Remove lid, and when cool enough to handle, finely chop leaves.
- Preheat oven to 375°F with rack in middle.
- While cabbage is steaming, peel and quarter potatoes. Generously cover potatoes with cold water in a 3- to 4-quart saucepan and add 1 teaspoon salt. Bring to a boil, then reduce heat, and briskly simmer, partially covered, until tender, 25 to 30 minutes.
- Drain potatoes well and mash in a large bowl with 3 tablespoons butter. Stir in cabbage, scallions, and salt and pepper to taste. Cool to warm and stir in egg.
- Melt remaining 2 tablespoons butter. Brush pie plate with some of butter. Spread potato mixture evenly in plate and brush with remaining butter.
- Bake until golden, about 35 minutes. Let stand 10 minutes before serving.