Cook the Potatoes:
Place the peeled and cubed potatoes in a large pot and cover them with cold water.
Bring the water to a boil and cook the potatoes until tender, about 15–20 minutes.
Drain the potatoes thoroughly and return them to the pot.
Mash the Potatoes:
Mash the cooked potatoes using a potato masher or ricer until smooth.
Mix the Ingredients:
Add butter, sour cream, heavy cream, 1 1/2 cups of shredded cheddar cheese, garlic powder, salt, and pepper to the mashed potatoes.
Stir until everything is well combined and creamy.
Assemble the Casserole:
Preheat your oven to 375°F (190°C).
Spread the mashed potato mixture into a greased 9x13-inch baking dish.
Sprinkle the remaining 1/2 cup of shredded cheddar cheese evenly over the top.
Bake:
Bake the casserole in the preheated oven for 20–25 minutes, or until the cheese is melted and bubbly.
Garnish and Serve:
Remove the casserole from the oven and garnish with fresh chives if desired.
Serve hot and enjoy!