Preheat oven to 350°F (177°C). Line a large baking sheet with parchment paper or a silicone baking mat. Set aside.

In a medium bowl, whisk the flour, quick oats, baking soda, and cinnamon together. Set aside.

Using a handheld or stand mixer with a paddle attachment, beat the butter on high speed until creamy, about 1 minute. Scrape down the sides and the bottom of the bowl as needed. Switch the mixer to medium speed and beat in the brown sugar until combined. Beat in the egg and vanilla extract, scraping down the sides and bottom of the bowl as needed. Turn the mixer off and pour the dry ingredients into the wet ingredients. Turn the mixer on low and slowly beat until a very soft dough is formed. The dough will be sticky.

Divide dough in half and place in opposite corners on the baking sheet, making sure to leave enough room around the edges for spread. Form the dough into two round balls using a spoon or your fingers. Bake for 20-22 minutes or until lightly browned on the edges. Remove from the oven and allow to cool for 15 full minutes on the baking sheet. Then transfer to a wire rack to cool completely. At this point, I placed my two cookies in the refrigerator to speed up the cooling process.

Using a handheld or stand mixer with a paddle attachment, beat the butter on high speed until creamy, about 1 minute. Scrape down the sides and the bottom of the bowl as needed. Switch the mixer to low and slowly add the confectioners’ sugar. Beat for 1 minute. Add the cream and vanilla, then beat on high until creamy and combined. Add more cream to thin out or more sugar to thicken, as needed. Add a pinch of salt to cut the sweetness if desired.

Frost the underside of one cooled cookie and top with the second cookie. Enjoy!