See blog post for more details.
Feel free to use a combination of apples. I like to use Honey Crisp, Gala, Granny Smith etc. Leave the skin on the red apples. Just don't dice too large, this will make the pieces of skin a little intrusive. I like somewhere between a 1/4 and 1/2 inch dice.
Use the amount of milk you desire. More will create a thin almost transparent glaze. Less (or more sugar) will create a thicker ribbon glaze.
Here is the link to my Salted Bourbon Caramel Sauce
Recipe adapted from King Arthur Baking, here