Preheat your oven to 350 degrees. Line a large baking sheet with parchment paper.
In a medium bowl add the dry ingredients: almond flour, coconut flour, cinnamon, baking soda, and salt. Mix and set aside.
In a large bowl add the wet ingredients: egg, coconut oil, maple syrup, coconut sugar, vanilla and lemon juice. Whisk until fully combined.
Now pour the dry flour mixture into wet ingredients. Fold until combined. Set aside while you make your cinnamon sugar coating.
Make the cinnamon sugar coating by combining the coconut sugar and cinnamon in a small bowl.
Using a cookie scoop or a spoon, scoop the cookie batter into 14 balls, rolling each ball in the cinnamon sugar coating. Place the rolled cookies onto the baking sheet. Using your hand, lightly flatten each cookie (about ¼ inch thick).
Bake for 10-12 minutes. Let let the cookies cool while you make the filling.
Mix all the filling ingredients together in a small bowl until the icing forms.
Assembly the cookie sandwiches! Using a butter knife or an icing knife, spread the buttercream filling on the cookies. Sandwich them together and enjoy!