Wash and peel the potatoes carefully. Cut them into small cubes for even cooking. Try to keep the pieces similar in size. This helps them cook at the same speed. Set them aside in a bowl.

Take a large mixing bowl. Add sour cream, milk, and melted butter. Mix everything until smooth and creamy. This base gives rich flavor to the potatoes. It also helps them stay soft.

Add chopped onion, garlic powder, salt, and black pepper. Mix well so every bite has flavor. The onion adds a slight sweetness. Garlic gives a warm, savory taste.

Add diced potatoes into the creamy mixture. Stir gently to coat every piece well. Make sure all potatoes are covered. This step is important for even flavor.

Grease your crockpot lightly with butter. Pour the potato mixture into the crockpot. Spread it evenly using a spoon. This helps even cooking.

Sprinkle cheddar cheese over the top. This will melt slowly and blend with potatoes. Do not mix too much now. Let the layers stay slightly separate.

Cover the crockpot with a lid. Cook on low heat for 4 hours. Avoid opening the lid often. This keeps the heat inside and cooks evenly.

In the last 30 minutes, add mozzarella cheese on top. Cover again and let it melt. This gives a stretchy, creamy finish.

Once done, sprinkle fresh parsley on top. Let it cool for a few minutes. Serve warm and enjoy every bite.