Mom's Fish Chowder

Ingredients (9)

• + 2 tablespoons butter, or more to taste add to pantry
• + 1 sweet onion (such as Vidalia®), diced add to pantry
• + 1 ¼ cups water, divided add to pantry
• ✓ 1 pound cod fillets
• + 1 large russet potato, peeled and cut into cubes add to pantry
• + salt and ground black pepper to taste add to pantry
• + salt and ground black pepper to taste add to pantry
• + 1 cup whole milk add to pantry
• + 1 cup evaporated milk add to pantry