Whisk the cream and cream cheese in the saucepan over medium heat until smooth. Stir in 1½ cups shredded cheese (save the other ½ cup to sprinkle on top). Continue warming until sauce is smooth and thick. Season with salt, pepper, and optional mustard or garlic.
⅓ cup heavy whipping cream, 2 ounces cream cheese, 2 cups cheddar cheese, 1 teaspoon salt, ¼ teaspoon ground black pepper, ½ teaspoon Dijon mustard, ½ teaspoon garlic powder