In a 10-inch cast iron pan, melt butter over medium heat. Whisk in both sugars and vanilla. Cook until the sugar is dissolved.
Remove from the heat and allow to cool slightly before adding the the whole egg and the egg yolk. Stir to combine. Add in the flour, salt, and baking soda. Stir until fully mixed.
Spread the cookie evenly in the pan. Dollop the peanut butter on top of the cookie ad using a butter knife or a toothpick, swirl the peanut butter throughout. Gently fold in the chocolate chips.
Bake for 16-18 minutes until the edges turn golden brown and a toothpick inserted in the middle comes out clean. Allow to cool slightly and serve with your favorite ice cream!