1Combine flour, baking soda, baking powder, cinnamon, and salt. Mix and set aside.
2In a mixer, cream together butter, coconut oil, dark brown sugar, and maple syrup until well combined.
3Add vanilla extract, one large egg, and one egg yolk. Mix well.
4Gradually add the dry ingredients to the wet ingredients and mix until well combined.
5For the filling, combine dark brown sugar, melted butter, and cinnamon. Mix well until a thick consistency is achieved.
6Take half a scoop of cookie dough, press down the center, add a teaspoon of the filling, top with another half scoop of dough, and press the sides to seal.
7Flatten the cookie dough balls slightly and refrigerate for a couple of hours until hardened.
8Bake cookies at 350°F (175°C) for 12-14 minutes.
9For the icing, whisk together powdered sugar, salt, cinnamon, and milk until smooth. Add more milk if needed to reach desired consistency.
10Once the cookies have cooled, ice them with the prepared icing.