Add potatoes to a large pot. Fill with cold water to cover slightly over potatoes. Boil until tender, about 15 to 20 minutes depending on the size of your potatoes. Drain. Return potatoes to pot.
Mash potatoes, butter, sour cream and salt. Stir in half the cheese and ½ cup of green onions. Spread mixture in a 9x13 baking dish.
Sprinkle remaining cheese and bacon on top.
Bake at 400°F for 15 minutes or until cheese melts. Sprinkle with remaining green onions.
Notes
Make-Ahead: Prepare as directed until just ready to bake. Cover and refrigerate for up to 1 day. Bake as directed.