Preheat the oven to 350 degrees F.
Line a 15 x 10 inch jellyroll pan with parchment paper and lightly spray it with cooking spray.

Pulse 1 cup of butter, flour and sugar in a food processor.
You want the mixture to come together to form small crumbs, but don't over mix it.

When grab a handful of the mixture you should be able to slightly shape it like dry clay.
I usually pulse the mixture about 15 times.

Do not over mix the dough. It is okay to see small pea sized chunks of butter.
This is what gives the cookie it's light, delicate texture.

Press the mixture into the jellyroll pan and prick the dough with a fork a couple of times.

Bake for 15 - 20 minutes or until the top is slightly golden brown.

While the shortbread is cooking, make the caramel.
Stir the remaining butter, condensed milk, bourbon and corn syrup in a heavy saucepan over low heat.

Continue to stir until the butter in melted.
The key to making caramel is low and slow.
Add brown sugar and stir constantly for 20 to 30 minutes.

The caramel will start to thicken and become light brown.
Take the caramel off the heat at this point because you don't want to over cook it or it will set too hard when it cools.
Pour caramel over the shortbread layer and chill for 30 minutes.