Cream together the butter and brown sugar until light and fluffy, about 5 minutes.

Add the egg and vanilla. In another bowl, whisk together flour, oats, baking soda, salt, and cinnamon. Slowly add the to the butter mixture. Mix until just combined.

Use an ice cream scoop to drop dough balls on a parchment-lined cookie sheet. If you do not have an ice cream scoop, make them into 1 tablespoon sized balls.

Bake in a preheated 375 degree oven for 8 to 10 minutes. Let cool completely on a cooling rack.

Make the filling by creaming together the butter and marshmallow creme. Slowly add the powdered sugar and vanilla. Beat until smooth and fluffy.

Add a generous scoop (I used the same scoop that I used to measure out the dough) of filling to half of the cookies.

Add another cookie to the top and there you have an oatmeal cream pie.