Preheat the oven to 350°F. Grease a 12-inch cast-iron skillet with butter.
In a medium mixing bowl, whisk together the flour, baking powder and salt. Set the bowl aside.
In a stand mixer fitted with the paddle attachment, cream together the butter with the sugar and light brown sugar.
Add the eggs, one at a time, beating until combined, then beat in the vanilla extract.
Add the flour mixture into the stand mixer and mix just until the dough comes together. Beat in the chopped candy until combined.
Scrape the dough into the skillet, then sprinkle it with the sea salt.
Bake the cookie until it's almost fully baked but still slightly underdone in the center, 30 to 35 minutes.
Remove the cookie from the oven and allow it to cool for 10 minutes before serving topped with ice cream.