In the bowl of a stand mixer fitted with a paddle attachment (or using a hand mixer), cream butter. Add brown sugar and granulated sugar. Mix until smooth. Add egg, molasses, and apple sauce.
In a bowl, whisk together flour, cinnamon, baking soda, baking powder and sea salt. Add to mixing bowl. Fold in rolled oats and walnuts.
Use a 1 ½- inch scoop to portion out cookies. Arrange on parchment lined baking sheet at least 2 inches apart. Bake for 13-15 minutes, rotating pans midway through baking. Allow to cool in pan for 3 minutes before transferring to wire rack to cool to room temperature.
Maple Glaze: Whisk together powdered sugar, maple syrup, salt and milk until smooth. If glaze is too thick, add additional milk 1 tsp at a time until desired consistency is achieved. Drizzle glaze over cooled cookies. Enjoy immediately, or allow glaze to harden and set.
Notes
Store cookies in an airtight container at room temperature for up to five days. However, they are best enjoyed within three days after baking.