Line a 9-inch pie dish with parchment paper, leaving overhang along the sides. Scoop the Nutella into the dish and spread evenly into a 7-inch diameter circle. Freeze for at least 1 hour, or until solid.
Using paper overhang, remove Nutella disc onto a plate, peeling the parchment paper off of the disc. Return Nutella slab to the freezer.
In a medium saucepan, melt the butter over medium-low heat. As the butter melts, it’ll start to foam, then turn a clear golden color. Continue to stir the butter, scraping up any browned specks from the bottom of the pan as it starts to brown. It should have a nutty aroma. Once browned and nutty, remove from the heat and transfer to a mixing bowl to prevent it from cooking (and possibly burning) any further.
Using a wooden spoon, stir both sugars into the browned butter until completely incorporated. Add the eggs and vanilla and continue stirring until combined. Add the flour, baking soda, salt and cornstarch, stirring until just incorporated. Stir in the chocolate chips/chunks*. Cover and refrigerate dough for at least one hour.
Preheat the oven to 350ºF and grease a 10-inch cast iron skillet.
Press half of the dough into the skillet. Place the frozen Nutella disc on top of the dough. Cover with the remaining dough by pressing portions of dough between your palms, then piecing them together on top of the Nutella disc.
Bake for 20-22 minutes, or until the edges are golden brown. Pizookie will continue to bake as it cools. Immediately press more chocolate chips/chunks into the top of the pizookie.
Allow the pizookie to cool for 20-30 minutes before slicing into the cookie.** Slice and serve with a scoop of ice cream on top!