Preheat oven to 350. Line a 13x9 glass baking dish with parchment paper so it hangs over the edges

For the shortbread layer: In your mixer bowl, cream the 1 cup of butter with the sugar for about 3 minutes

Add the egg yolk and the vanilla. Continue mixing until well combined

Add the flour and mix until just combined

Spread the dough into your prepared pan and use your fingers and palms to press into an even layer on the bottom

Bake at 350 for 18-20 minutes or until the edges start to turn golden brown

For the caramel: In a large saucepan, over medium heat, add the 1/2 cup butter, brown sugar, condensed milk, corn syrup, vanilla, and 1/4 tsp salt .

Stir gently over medium heat and continue stirring while it bubbles and starts to get darker. If you are using a candy thermometer it is done at about 225 degrees. If you aren't, watch for it to start thickening and pulling away from the side. It should take about 4-5 minutes.

Pour the caramel on to your baked base and use an offset spatula to spread it to the edges.

Let the caramel set before making the chocolate. (You can let the pan come to room temp, then put it in the refrigerator to speed it up setting.)

For the chocolate layer: Melt your chocolate chips with the heavy cream in the microwave. Do 30 seconds at a time until it starts to melt, then stir until smooth and silky.

Pour the chocolate over the caramel layer and use an offset spatula to spread to the edges.

Sprinkle with a little sea salt, (optional), then chill before cutting in to squares.