Lightly spray a 9x13 rectangle pan with non-stick cooking spray. You want this to be very light so if you have any puddles forming, use a paper towel to wipe away any excess.

In a large microwave safe mixing bowl, heat the butter and marshmallows on high for 2 minutes. The butter will be melted and the marshmallows will be very puffy. Stir together to make sure that everything is melted.

Add the vanilla extract and the rice krispies and stir until the cereal is completed coated in marshmallow.

Use a spatula or your fingers to press the rice krispie treats into the prepared pan. If you wet your fingertips, the marshmallow will not stick to your fingers. Set aside while we make the caramel.

In a medium saucepan, combine the sweetened condensed milk, butter, brown sugar, corn syrup, vanilla extract and salt. Whisk together and heat over medium-low heat, stirring continuously. When it starts to bubble, it will start to thicken. Continue to stir and cook for 4 minutes after you start to see the first bubble. Remove from heat to cool in the saucepan for 10 minutes. It will continue to thicken while it sits.

After the five minutes, whisk the chocolate smooth.

Let stand for 20 minutes to full set before slicing and serving.