Preheat your oven to 350 degrees F and line a 9x9 inch baking dish with parchment paper.
Cream the butter then add the sugar, salt and beat until light and fluffy. Add the vanilla then mix until combined. Add the flour a little at a time and mix untill it is combined and it forms a ball. Don't overwork it.
Transfer your shortbread mix to your prepared pan and press into an even layer then bake at 350 degrees F for about 25 minutes or until the edges are golden.
While the base bakes prepare the caramel. You may want to use a candy thermometer but you don't need one. In a saucepan combine the butter, brown sugar, salt, vanilla, sweetened condensed milk.
Place the saucepan over medium heat and whisk until melted and combined then continue whisking over the heat while the caramel bubbles and darkens to a richer colour. Once the caramel reaches 225 degrees or if it starts to thicken and pull away from the edge, 10 to 15 minutes, your caramel is ready. Careful to continue whisking so it does not burn on the bottom.
Pour the caramel mix onto the shortbread base, smooth to the edges creating a flat layer. Chill for about 15 minutes so the caramel sets.
Chop chocolate and melt with cream either in a double boiler stirring throughout. Pour the chocolate over the caramel and smooth into an even layer. Sprinkle with salt then chill. Once the squares have chilled you can cut them into 1 inch pieces.
These bars can be kept in the freezer for a couple of months. Simply cut into one pieces and wrap them well with plastic wrap before you freeze them.