Place potatoes in a large pot and add enough water to cover. Cook until soft. Drain.
Preheat oven to 350 degrees F.
Place potatoes in a large bowl. Add butter, half and half and sour cream. Whip using hand mixer.
Add 1 cup cheddar cheese, garlic powder, pepper and parsley. Stir well.
Transfer mixture into buttered 13" x 9" casserole dish. Spread evenly. Top with remaining cheddar cheese.
Bake casserole for 35 to 38 minutes. The edges will be golden brown.
Garnish with chopped bacon and parsley. Serve.
Video
Notes
To make ahead of time: cover casserole dish with mashed potatoes mixture and store in fridge for up to 2 days. Top with shredded cheddar just before baking.