Preheat the oven to 325°.
Butter a 1 1/2-quart casserole dish. Place the potatoes in a 3-quart saucepan; cover with cold water. Add 1 tablespoon of the salt and bring to a boil. Cover the potatoes, reduce the heat, and cook for 20 minutes or until fork-tender. Drain the potatoes. Put pan back on burner for 1 minute, shaking the pan until the potatoes are dry. Mash the potatoes with potato masher or mixer. Add the butter, sour cream, cheese, chives and remaining 1/2 teaspoon salt. Mash or stir until mixed well. Spoon the mixture into a casserole dish.
Bake the potatoes for 20 to 25 minutes or until hot. Remove from the oven and sprinkle with the onions and cooked bacon pieces. Return the dish to the oven and bake for an additional 5 minutes.