In a large mixing bowl, whisk together maple syrup, coconut oil, egg, yogurt, and vanilla until combined. Add oats, oat flour, cinnamon, baking soda, and salt. Use a wooden spoon or spatula to combine until a pretty soft dough forms. Refrigerate dough for 25-30 minutes to set (this is important!).

Preheat oven to 350°F. Line a large baking sheet with parchment paper.

Use a ~1.5 cookie dough scoop to portion dough onto prepared baking sheet. Slightly flatten dough using the palm of your hand. Bake for 10-11 minutes until light golden brown. It's important you don't overbake so you get the perfect soft texture!

Cool cookies on the baking sheet for 5 minutes before transferring to a wire cooling rack to cool completely.

Use a handheld mixer to combine all filling ingredients until creamy. Top half of the cooled cookies with the filling. Sandwich the filling with the remaining cookies.