Preheat oven to 350°F.
In a small bowl, sift together the flour, baking soda, baking powder, and salt. Set aside.
In a separate medium bowl, cream together the melted butter, brown sugar, and white sugar for a few minutes until light brown.
Add in the egg + egg yolk, peanut butter, and vanilla extract. Mix until completely combined.
Slowly incorporate the dry ingredients into the wet ingredient bowl. Fold in your chopped chocolate bar.
Prepare an 8-inch cast iron skillet with parchment paper or non-stick spray, then add in the cookie dough into an even layer.
Bake the cookie skillet for 20 minutes; it will just start to turn golden brown.
Let the cookie rest for 5 minutes, then remove from the skillet to stop it from cooking.
Top with vanilla ice cream or salted caramel drizzle and dig in. Enjoy!