Preheat oven to 350 degrees and very lightly grease a 10" cast iron skillet.

In your mixer with with paddle attachment, beat together 1/2 cup butter, 1/2 cup sugar, and 1/2 cup of brown sugar. Add in the 1/3 cup of peanut butter and whip ingredients together on medium speed until combined.

Next, add in the egg, 1/4 cup of milk, and 1/2 tsp of vanilla, continue mixing at medium-high speed until the color of the mixture lightens and turns fluffy about 3 minutes. You may have to scrape the sides to ensure the peanut butter is getting fully incorporated.

Finally, pour in 1 cup of oatmeal, 1 cup of all-purpose flour, and a 1/2 tsp of baking soda. Mix batter until everything is combined.

Using a rubber spatula, scrape the mixture into the cast iron skillet and evenly spread it around the pan.

Place on the middle rack of the oven and back for 30 minutes, or until golden brown and the sides and middle have risen. If poked in the middle with a toothpick, the toothpick should come out clean.

Immediately after the skillet comes out of the oven, pour 1 cup of chocolate chips evenly over the top and allow them to sit for at least 10 minutes.

While the chocolate chips are melting, in a small container with a tight-fitting lid, combine 1/4 cup powdered sugar, 3 tbsp of peanut butter, and 3 tbsp of milk. Place the lid on tight and shake the contents for a couple of minutes until they are combined.

After 10 minutes, use a butter knife to spread the melted chocolate chips evenly around the top of the skillet cookie. 

Pour the peanut butter frosting into a small ziplock bag and cut the tip off of one corner. Evenly drizzle the peanut butter frosting over the top of the melted chocolate.

For a pretty design, use a toothpick to draw lines through the frosting.

This skillet cookie is delicious served warm and gooey. But also has a nice chocolate snap once the topping has cooled and set!

Enjoy!