This is a regular dish in our household! My kids loved it and quickly ate up the leftovers the following morning!

Instructions:
Preheat oven and prepare baking dish: Preheat your oven to 375°F (190°C). Line a baking dish with aluminum foil.
Cook the potatoes: Place the cubed potatoes in a large pot and cover with cold water. Add a pinch of salt and bring to a boil over medium-high heat. Cook until the potatoes are tender, about 15-20 minutes.
Mash the potatoes: Drain the potatoes and return them to the pot. Add the milk, butter, and sour cream. Mash until smooth and creamy.
Stir in cheddar cheese: Stir in the shredded cheddar cheese, salt, and pepper. Mix until the cheese is melted and well incorporated.
Transfer to baking dish: Transfer the mashed potato mixture to the prepared baking dish. Smooth the top with a spatula.
Add topping: Sprinkle the grated Parmesan cheese and breadcrumbs evenly over the top.
Bake: Bake in the preheated oven for 20-25 minutes, or until the top is golden brown and crispy.
Cool and garnish: Remove from the oven and let cool slightly before serving. Garnish with chopped chives if desired.