Preheat oven to 350.

Grease a 2-1/2 quart casserole dish with nonstick cooking spray and set aside.

Boil peeled and cut potatoes in water until tender. There is no need to perfectly boil for shape retention as these potatoes will be smashed down. Once fork tender, move onto next step.

Drain water and set aside cooked potatoes.

Add 1-1/2 sticks butter and heavy whipping cream to a saucepan.

Heat pan on medium low heat, stirring frequently until butter is melted and mixture is hot, but not boiling.

Add cooked potatoes and mash down with a potato masher.

Add in sour cream and beat well with a mixer (on low) until smooth.

Fold in 1 cup Parmesan cheese and 3 sliced green onions.

Season potatoes with salt and pepper and mix well again.

Pour potatoes into prepared baking dish.

Slice remaining butter into pats and add on top of potatoes.

Sprinkle top of potatoes with remaining 1/2 cup Parmesan cheese.

Bake for 15-18 minutes until hot and bubbly around the edges.

Broil for 1- 2 minutes for top to brown. (please watch carefully as broiling moves fast in a hot oven)

Sprinkle top with additional green onions before serving.