Preheat oven: Preheat oven to 375°F.
Mix: In a large bowl stir together peanut butter, coconut sugar and egg. Add vanilla, oats, oat flour, baking soda and salt. Stir to combine.
Scoop and form: Using a 1/2 tablespoon, scoop cookie dough and roll into a ball. Place on an un-greased baking sheet, gently press each cookie down a tiny bit and bake for 8-10 minutes or until the bottoms are lightly browned.
Let cool: Remove and let cool on baking sheet for 4-5 minutes, then transfer to a wire rack to cool completely.
Make filling: While cookies are baking, make the peanut butter filling by stirring together peanut butter, maple syrup and oat flour.
Make sandwich cookies: Once cookies are cool start making the sandwiches. Spread a little of the peanut butter filling on the bottom of one cookie and then gently press the bottom of another cookie on top. Repeat until all cookies are sandwiched. If you happen to have an odd number of cookies, that just means that you can eat one while making these. :)
Enjoy: Once sandwiched, the cookies are ready to serve!
Store: Store leftover cookies in an airtight container at room temp for 3-4 days, in the fridge for 5-7 days or the freezer for 3 months. Cookies are best served right away if you like crisp cookies. They will soften as they age.