Preheat oven to 350°F. Line two baking sheets with parchment paper.
In a small cup, mix the ground flaxseed meal and water. Set aside to thicken while you prepare the rest of the ingredients.
In a stand mixer or with electric beaters, mix the coconut oil, maple syrup, and vanilla on medium speed for about 5 minutes, until smooth.
In a separate bowl, whisk together the almond flour, arrowroot starch, coconut flour, salt, and baking powder.
Add the flax mixture and the dry ingredients to the mixing bowl with the wet ingredients. Mix until a thick dough forms.
Gently fold in the lemon juice and lemon zest.
Scoop the dough onto the prepared baking sheets, leaving about 2 inches of space between each scoop (they do not spread very much).
Place the extra ⅓ cup arrowroot starch onto a plate or piece of parchment. Roll each dough ball in the arrowroot to coat completely, then place it back on the baking sheet.
Repeat the coating step one more time, starting with the first dough ball you rolled. This helps create the crinkle-top effect.
Gently press each dough ball down with two fingers to flatten slightly. Don’t handle them too much or the crinkles won’t form as well.
Bake for 12–14 minutes, until the tops are crackly and the cookies look set.
Let cookies cool on the baking sheet for at least 10 minutes before moving them — they’re delicate when hot.