Preheat oven to 350 degrees. Lightly grease a shallow 2-quart baking dish.
Cook potatoes in a large pot with salted water to cover for 20 to 25 minutes, until tender when pierced. Drain well and return to pot. While potatoes are still hot, add butter and mash with a potato masher until smooth. Stir in 1 cup of cheese, milk, sour cream and eggs until blended. Then add 1/2 cup of scallions, 3 slices of bacon, crumbled; salt and pepper to taste.
Spoon into the prepared baking dish. Sprinkle with remaining cheese and 2 slices of bacon, crumbled.
Bake uncovered for 35-40 minutes or until the top is lightly golden brown. Sprinkle with remaining 1/4 cup of scallions and serve.