Whisk together almond flour, oat flour, baking soda, cinnamon, and nutmeg in a large bowl; set aside.
In a stand mixer, cream butter (or coconut oil), maple syrup, apple butter, and vanilla extract until smooth.
Gradually add the flour mixture and mix until a dough forms. Cover and chill for 30 minutes.
Preheat oven to 350°F and line baking sheets with parchment paper or silicone mats.
Roll dough into 20 small balls. Set up an assembly line with egg white in one bowl, walnuts in another, and the baking sheet.
Dip each ball into egg white, then roll in walnuts, shaking off excess. Place on baking sheet.
Press a small well into each cookie with a measuring spoon or your finger. Fill wells with apple jelly.
Bake for 15–18 minutes until edges turn light brown. Cool on pan for 5 minutes, then transfer to a wire rack.
Whisk powdered sugar, maple syrup, and water to make icing. Drizzle over cooled cookies. Enjoy!