Preheat the oven to 350° F. Line a pan with parchment paper or a silicone liner and set aside.

Cream together the butter, brown sugar and granulated sugar until light in color and fluffy in texture.

Add the egg and mix until combined.

Add the flour, rolled oats, cinnamon, baking soda and salt. Mix until a sticky dough forms.

For medium sized cookies, use a #40 scoop (1 ½ tbsp of dough for each scoop) and for large cookies, use a #24 scoop (3 tbsp of dough). Arrange on the prepared cookie sheet. These cookies will flatten and spread, so make sure to leave room for them to do so.

Bake at 350° F until the cookies have flattened, the center no longer looks wet and the edges start to turn golden brown. For the medium sized cookies, 7-9 minutes. For the large cookies, 9-11 minutes. Allow the cookies to cool completely on the pan.

Once the cookies have cooled completely, make the vanilla frosting by first creaming the butter until smooth.

Add the powdered sugar one cup at a time, adding a little bit of heavy cream after each cup of powdered sugar to help incorporate the powdered sugar into the butter.

Repeat previous step until all of the powdered sugar has been added to the bowl and is completely incorporated.

Add the vanilla and mix thoroughly.

Add more heavy cream until you reach your desired consistency.

Either spread the frosting in onto the bottom of one cookie before sandwiching it with another or add the frosting to a piping bag and pipe the frosting in a swirl onto he bottom of one cookie and then sandwich with the second cookie.

Store at room temp for up to 3 days, in the fridge for up to 1 week (I actually like these cookies best chilled!) or in the freeze for up to 3 months.