Begin by creaming the softened butter with the packed brown sugar until well combined.
Next, add the granulated sugar and Karo syrup, mixing thoroughly.
In a separate bowl, whisk together the dry ingredients: all purpose flour, baking soda, salt, cinnamon, and nutmeg.
Gradually combine the wet and dry mixtures, stirring until just mixed.
Gently fold in the quick oats until they are evenly distributed.
Preheat your oven to 350 degrees Fahrenheit and bake the cookies for approximately 10 minutes.
For the vanilla buttercream, cream together the unsalted butter and powdered sugar until smooth.
Incorporate the marshmallow cream, vanilla, and a pinch of salt, mixing until well blended.
Transfer the buttercream into a large ziploc bag for easy assembly.
To assemble the cream pies, take two cookies and press them together with the buttercream filling in between.
