• Preheat the oven to 350°. Line two 9x13 baking dishes with parchment paper and spray with nonstick cooking spray.

MAKE THE OATMEAL COOKIE LAYERS

• In a large bowl add the 2 ½ sticks of butter, brown sugar, and sugar and beat with a hand mixer until light and creamy (about 2-3 minutes).
• Add the eggs and vanilla and beat for 2-3 more minutes.
• In another large bowl, mix the flour, cinnamon, salt, and baking soda. Add the dry ingredients to the wet mixture and mix just until combined. Add the quick oats and old-fashioned oats to the bowl and mix just until combined.
• Scoop half the mixture into one of the lined 9x13 baking dishes and the rest into the other 9x13 and spray your hands with nonstick cooking spray. Flatten the dough with your hands, spreading evenly all the way to the corners of the baking dish.
• Bake for 13 minutes or until golden brown.

MAKE THE CREAM FILLING

• Let the bars cool while you make the cream. Add the butter to a large bowl and beat using the hand mixer until light and creamy. Add the powdered sugar and beat again until well mixed. Add the marshmallow fluff and vanilla and beat again until smooth.
• The bars must be completely cool before spreading the cream on top. Lift one of the bars out of the dish by lifting the parchment paper up and then placing the parchment paper lined bar on a tray or sheet pan. Spread the cream all over the top of the oatmeal bar. Lift the other bar out of the baking dish by the ends of the parchment paper. Carefully flip that bar on top of the cream and lightly press down.
• Place in the freezer for 1 hour. Take out and slice into bars, serve, and enjoy!