Here is the recipe:
1/2 cup + 1 Tbs. all-purpose flour
1/2 cup quick oats
1/4 tsp + 1/8 tsp baking soda
1/4 tsp cinnamon
1/4 cup unsalted butter, softened
1/2 cup brown sugar (packed)
1 large egg
1/2 tsp vanilla
1 cup butter, softened
1-7 oz jar marshmallow fluff
2 cups confectioner sugar
1 tsp vanilla
1 Tbs heavy cream or milk
Preheat oven to 350
Line the bottom of 8 inch round cake pan with waxed or parchment paper.
Mix flour, baking soda, cinnamon and quick oats in small bowl and set aside.
Cream butter, stir in brown sugar, scrape sides of bowl as needed, add egg and vanilla and stir until combined, I did this by hand instead of using a hand or my stand mixer. Stir in flour mixture, mix well and form into a ball with a spatula.
Scoop ball into center of cake pan and flatten a little, making it about an inch larger all around. I did the first 2 layers without flattening and it didn't quite fill the pan but was still good :)
Bake at 350 for about 20 - 22 minutes until edges are golden brown. The center of the cookie should not be shiny or wet.
I did 3 separate batches so I wouldn't have to mess around guessing how much to put in each pan but you can double or triple this and do it your own way. Make sure you stay under 1/2 tsp of baking soda per batch or it rises too much, check out bottom layer in pic, I got distracted and spilled a little baking soda, it's quite a bit thicker than the first two.
For the filling, cream softened butter with hand mixer or in stand mixer for about 2 minutes, add marshmallow cream, powdered sugar and vanilla, mix on low until incorporated and then on medium until desired consistency. Add 1 tablespoon of heavy cream, half and half or milk if needed. This makes enough to generously frost two layers with some leftover. You could also frost sides and top but you don't need to.
This has a really nice taste with a little crunch around the edges but is not as soft as the Little Debbie oatmeal cream pie cookie. I think the icing could use more marshmallow and less butter which I'll try next time but tastes wonderful as is!
I'm going to try making these as individual cookies and will post the results along with the size ball of batter and baking time you will need.