Preheat oven to 350 degrees.  Make foil sling for a 13 x 9 inch baking pan for easy removal of bars later.

Combine flour, sugar and salt into a medium bowl.  Add melted butter and stir with a rubber spatula until flour is evenly moistened.  

Crumble dough evenly over the bottom of the prepared pan.  Use your fingertips and palm to press and smooth the dough into an even layer.  Using a fork, pierce the dough at 1-inch intervals.  Bake until light golden brown, 25-30 minutes.

When finished, transfer pan to a wire rack.  Take a sturdy metal spatula and use it to press on the entire surface of the crust to compact it (this is to help make the finished bars easier to cut).  Let crust cool until just warm, at least 20 minutes.  

Begin to heat granulated sugar in a medium saucepan over medium heat, stirring constantly with a high heat-resistant silicone spatula or wooden spoon. Sugar will start to form clumps and eventually melt into a thick brown, amber-colored liquid as you continue to stir. Don't burn it!

Once the sugar is completely melted, immediately stir in the butter until melted and combined. I recommend cutting the butter into slices before adding! The caramel will bubble rapidly when the butter is added. Sometimes the butter will separate from the sugar, so remove from heat and vigorously whisk to combine it again, before heating it on the stove again.

After the butter has melted and combined with the melted sugar, stir constantly as you very slowly pour in the heavy cream. The mixture will bubble very quickly when added. After all the heavy cream has been added, stop stirring and allow to boil for about a minute. It will rise in the pan as it boils.

Remove from heat and stir in the salt. The caramel will be a thin liquid at this point. Allow to slightly cool down before using. Once it thickens (it may take a few minutes), then continue with the next part of the recipe.

Pour the slightly cooled and thickened salted caramel over the shortbread crust. Allow to cool and set completely before topping with the chocolate layer. You can speed up the process by putting it in the fridge!

Melt the chopped up chocolate and coconut oil in the microwave in short 15 second increments, stopping and stirring until completely melted.

Pour over cooled caramel. Top with sea salt if you'd like. Put in the fridge to set up completely before cutting into bars.

I recommend bringing the bars to room temp before cutting otherwise your chocolate will snap when you start to cut into it and not cut cleanly. You can store at room temp for a week or a few weeks in the fridge!