Funeral Potatoes

Name: Funeral Potatoes
Ingredients: 6 tablespoons butter, divided; 3/4 cup onion, diced; 2 cloves garlic, minced; 12 small potatoes, parboiled and shredded, or one (30-ounce) bag of frozen, shredded hash brown potatoes, thawed; one 10.5-ounce can condensed cream of chicken soup; 1 cup sour cream, or plain Greek yogurt; 1/4 cup grated Parmesan cheese; 1 teaspoon salt; 1/2 teaspoon ground pepper; 2 cups firmly packed shredded sharp cheddar cheese, divided; 1 1/2 cups crushed cornflake cereal or panko bread crumbs