Preheat oven to 325°F. Lightly grease oven-safe, 10-12" cast iron skillet (oven safe).
In mixer bowl with a paddle attachment, beat the butter until creamy. Add in granulated sugar & brown sugar then beat on medium-high until light & fluffy.
Beat in eggs, vanilla & milk on high speed until well mixed.
Scrape down the sides and bottom of the bowl as needed to be sure all is mixed in.
Add flour, cornstarch, baking soda, and table salt on low speed until combined. Add the colored chocolate candies & mix on low.
Transfer ½ the cookie dough into the prepared skillet & press down into an even layer. Add ½ Cow Tales caramel pieces & sea salt.
Top with remaining dough, pressing down again & then add the remaining Cow Tales caramels & sea salt.
Bake for 25-30 minutes or until browned on the sides and lightly brown on top.
Allow the cookie to cool slightly in the pan on a wire rack before serving. Serve with extra Caramel Creams, whipped cream, or ice cream if desired!