Preheat the oven to 350 degree. Soften the 9 tablespoons butter in the microwave for 30 seconds or until partially melted. Soften the remaining 8 tablespoons for 10 seconds or until you can make an indent with your finger.
Mix the butter and sugar together with an electric mixer until creamed. Add the vanilla and maple syrup and mix again until smooth. Add the eggs; beat slowly until incorporated. Add the flour, baking soda, and salt (sometimes it helps to add the flour in batches). Mix until a smooth dough forms. The dough should feel dry to the touch – if it sticks to your hands, add a few more tablespoons of flour. I generally try to err on the side of more flour. Stir in the chocolate chips. Melt the caramel pieces and heavy cream in the microwave for 2 minutes. Stir well until melted and smooth.
Press half of the dough mixture into a 9-inch or larger cast iron skillet lined with parchment paper. Pour the caramel over the dough and smooth with a spoon. Cover with another layer of cookie dough. Bake for 15-25 minutes (see notes). Remove from oven, sprinkle with sea salt, and allow to rest for at least one hour in order for the pieces to hold their shape when cut.
I baked mine uncovered for 15 minutes, but you could also cover with foil and bake for an additional 10-15 minutes to get the cookie center baked even further. If you only bake for 15 minutes total, like I did, the cookie WILL be underbaked. Cause that’s how we like it.