Follow with both sugars and mix. Blend eggs until smooth and set aside.
To a separate bowl add oats then sift flour, cocoa, cornstarch, baking powder and soda, salt, and spice.
Mix in the wet into the dry until smooth with a hand mixer.
****Drop cookie dough onto ungreased baking sheets. Bake at 350 for 8-9 min; 10 min if making jumbo cookies. Don't over bake! Allow to cool before moving to a wire rack.
Soften the cream cheese and butter to room temp (let it sit out for an hour) and cream.
Add a pinch of salt (1/8 tsp), vanilla, and marshmallow fluff and mix until creamy.
Incorporate 1 cup of powdered sugar at a time, fully incorporating before adding the next.
Sandwich a generous amount of filling between 2 cookies. Pies can be stored in the fridge or freezer for a few days.
Cookies*Bread flour can be substituted for all-purpose flour. The bread flour adds more gluten that gives the cookies a little more structure. Without it, the cookies are a bit thinner but still structurally sound.**Regular cocoa may be substituted.***Light brown sugar can be used instead but the dark, I found gave a richer color and taste.****This recipe will make at least 4 dozen cookies using a 1 1/2 tablespoon cookie scoop if evenly measured.Filling*Add 1-2 additional cups of powdered sugar for a firmer filling. 4 1/2 cups is perfect for piping onto cupcakes.Recipe adapted from Cooking Classy