Preheat oven to 350ºF.
If your cast iron skillet is well seasoned you probably don’t need to grease it; if it’s not well seasoned or you want to be sure the cookie comes out easily, lightly grease your skillet. (I use a 10″ skillet).
In a stand or electric mixer, beat the butter and sugars until light and fluffy.
Add eggs and vanilla, continue to beat until well combined.
Add in the baking soda, cinnamon, and salt beating until mixed in.
Gradually add in the flour and oats, then the chocolate chips.
Divide the cookie dough in half and press half of the cookie dough into the bottom of the skillet.
Top with 3/4 cup of the peanut butter (use an off-set spatula for easier spreading), and chocolate bars (I broke mine into pieces and then placed them on).
Place remaining dough on top – I did this in pieces, flattening out small pieces in my hand and setting them on. The pieces can touch, but don’t have to, the dough will spread as it bakes.
Add the remaining 1/4 of peanut butter, dropping in random spoonfuls around the dough. Use a butter knife to swirl the peanut butter as best you can.
Bake for 25-30 minutes or until the top is golden.
Serve while still warm with some vanilla ice cream!
*Old Fashioned or Quick Oats both work fine in this recipe, I've used both. Old fashioned oats will give you chewier oats and more texture to the cookie, quick oats will blend a bit more into the dough. So it's just personal preference on texture for what you use!