Spray a deep sided casserole dish with non-stick spray. Cut potatoes into 1/4" rounds. Make 2 layers of potatoes by shingling them on the bottom. Put Salt, Pepper and Parmesan Cheese on the potatoes. Put a light layer of the Spinach or Basil on this layer and a light layer of the Mexican Blend cheese on top. Pour a small even layer of the heavy cream over the top. Continue this process in separate layers until you reach the top of the casserole dish.
If you want a cheese sauce for individual servings: Put 1-2 cups of the Mexican Blend shredded cheese into a sauce pan over LOW heat. When the cheese starts to melt, pour in the heavy cream and use a whisk until you get a smooth, creamy texture.