Boil potatoes with the garlic and broth added to the approximate 2 cups of water to cover the potatoes until tender.
Preheat oven to 400 degrees. Butter baking dish.
Set aside 3/4 cup of potato water then drain cooked potatoes. Return potatoes to the pot and set on medium heat. Toss potatoes until dry and remove from heat.
Mash potatoes adding as needed reserved potato water.
Add sour cream, butter, salt, pepper and remaining water.
Beat until fluffy.
Stir in half of green onions or scallions and 1/4 cup Parmesan cheese.
Put into basking dish.
Drizzle with olive oil.
Bake for 30 minutes.
Sprinkle remaining cheese and sliced green onion tops for garnish.