1 large yellow onion, chopped
3 pounds russet potatoes, peeled and chopped
4 cups chicken stock
2 cups milk, whole or 2%
1 1/2 teaspoon kosher salt
3/4 teaspoon ground black pepper
1 cup mozzarella cheese
1/2 cup sour cream
Bacon bits (optional)
Chopped chives or green onions (optional)
Sour Cream (optional)