Preheat oven to 350 and spray a 9 inch cast iron skillet with non-stick spray.
Combine flour, baking soda, salt, and oats together in a medium bowl and whisk together, set aside.
In a large bowl, using a mixer, cream together butter and sugars until light and fluffy.
Add in peanut butter, egg, and vanilla and mix together until well combined.
Add dry ingredients and chocolate chips to wet ingredients and mix until just combined.
Press cookie dough into your prepared skillet, but leave a ½ inch space between dough and skillet edge to allow the dough to spread out.
Press peanut butter cups into dough, as many as you like, but don't press them down deep, the cookie dough will rise, so you don't want them sunken into the cookie.
Bake 25-35 minutes until an inserted toothpick comes out clean and golden brown. The last 10 minutes you might opt to place tin foil on top of your cookie, if it looks like it's browning too quickly.
Transfer from oven and serve warm, with vanilla ice cream and chocolate syrup.