Preheat oven to 350 degrees F. Line a baking sheet with a silicone mat or parchment paper.
Make the flax egg in your KitchenAid mixer bowl or a large bowl by combining the ground flax with water. Stir and set aside for 5 minutes to thicken.
Then add the coconut oil and sugar to the bowl. Beat/cream for 2 minutes until well combined and smooth. Add the baking soda, baking powder, and salt. Mix until combined.
Add in the flour and slowly mix the batter together. After it starts to come together, I like to pulse my mixer a couple times until the flour is mixed in and to prevent over mixing. You can use a spatula if you’d like. If the dough looks too crumbly, add the almond milk one tablespoon at a time and pulse the mixer again until dough comes together. It is supposed to be a thick (and maybe a tiny bit crumbly) dough. Fold in the walnuts.
Using a cookie scoop (about 1.5 Tablespoons), scoop dough into hand and roll into balls. Place on the lined baking sheet and flatten slightly. Gently press a walnut half into the middle of each cookie. Bake for 10-12 minutes or until slightly golden. Remove from oven and let it cool for 10 minutes on the cookie sheet. Transfer to a wire rack and cool completely. Enjoy!