Preheat the oven to 350°F (175°C).
Prepare the potatoes by peeling and dicing them into small cubes.
In a large bowl, combine the diced potatoes, sour cream, milk, half of the shredded cheddar cheese, diced onion, minced garlic, salt, and black pepper.
Transfer the potato mixture into a greased 9x13 inch baking dish, spreading it out evenly.
Sprinkle the remaining cheddar cheese on top of the potato mixture.
Mix the breadcrumbs with melted butter and sprinkle them evenly over the cheese layer.
Cover the baking dish with foil and bake in the oven for 30 minutes.
Remove the foil and bake for an additional 15-20 minutes, until the top is golden brown and crispy.
Once done, remove from the oven and let it cool for a few minutes before serving.