Preheat oven to 400°F. Spray the baking dish with non-stick spray.
Place potatoes in a pot. Cover with cold water completely.
Add 1 tablespoon salt to the water. Bring to a boil.
Boil potatoes for 20 minutes, or until fork-tender.
While potatoes cook, fry bacon until slightly undercooked.
Cool bacon on paper towels. Chop into 1/2-inch pieces.
Drain cooked potatoes. Return them to the pot.
Add butter and heavy cream to the potatoes.
Mash potatoes by hand until mostly smooth with small chunks.
Season potatoes with salt and pepper. Mix gently.
Transfer mashed potatoes to the baking dish evenly.
Top potatoes with shredded cheese and bacon crumbles.
Bake at 400°F for 10 minutes, or until cheese melts.
Sprinkle chopped scallions over potatoes before serving.