Set butter, sour cream and milk out on the countertop to worm up a bit
Wash, scrub and poke holes in all of the russet potatoes
Place potatoes on a baking sheet and bake at 400 degrees for 40 minutes, or until you can get a butter knife through them
While the potatoes are baking, cook bacon if you haven't already
Remove potatoes from oven, turn oven down to 350 degrees
Cut each potato into thirds or quarters, then mash as well as you can using a potato masher
In a large mixing bowl, combine potatoes, butter, milk, seasonings, 1 cup cheddar cheese and half of bacon
Stir well and place potato mixture into a sprayed 9x13 baking pan or dish
Top the casserole with reserved bacon and additional shredded cheese
Bake, uncovered, for 20-25 minutes. Top with sliced green onions and serve