Place 16 ounces Velveeta cheese in the center of a 9x13-inch baking dish.
Pour 16 ounces elbow macaroni around the cheese in the baking dish.
Pour 3 cups heavy whipping cream and 1 cup water evenly over the pasta.
Season with ½ teaspoon salt and ½ teaspoon black pepper.
Cut 4 tablespoons butter into 4 equal pieces and place one piece in each corner of the baking dish.
Cover the dish tightly with foil and bake for 45 to 60 minutes, or until the pasta is tender. If needed, add additional water near the end of the cooking time to prevent the pasta from drying out.
Carefully remove the pan from the oven and remove the foil.
Stir the pasta and melted Velveeta cheese together until creamy and well combined.
Add 2 cups shredded cheddar cheese, stirring 1 cup at a time until fully melted.