Preheat the oven to 350 degrees F. In a 13 by 9 inch pan grease lightly.
Combine in a bowl: brownie mix with melted butter, eggs, and milk. If mix is too thick add in a little more milk. Take out 3 cups of the batter and put it to the side. Then place the rest in the baking pan and cook half way done. Take them out and let cool slightly.
Caramel sauce: In a sauce pan over medium heat combine the brown sugar, heavy whipping cream, butter, and salt, stirring gently for 5 to 10 minutes until it is thicker. Add the vanilla and cook a minute longer. Take off heat and allow it to cool in a bowl.
When it is cool add in the toffee bits. Then pour the caramel sauce over the cool brownies. Then pour the left over brownie batter. It should cover the caramel sauce completely. Then back for 10 minutes more until bottom and top is completely done.