Preheat oven to 350°F. Line a 9x9 pan with parchment paper and set aside.
In a large bowl, mix melted butter and both sugars together until combined. Stir in the egg, egg yolk and vanilla until smooth. Add flour, corn starch, salt and baking soda and mix until just combined. Fold in chocolate chips by hand. Press half of the dough into the pan.
For the caramel filling, in a small saucepan on medium-low heat, add caramels and heavy cream, stirring until smooth. Pour caramel onto cookie dough.
Take remaining cookie dough and scatter it on top of caramel. Not to worry if there are open spots.
Bake for 22-25 minutes or until the top is lightly golden. Remove from oven, sprinkle with sea salt and place on wire rack to cool completely before cutting into them. If you cut them too soon, the caramel will ooze!