Line a baking pan with parchment paper and preheat the oven to 350°F (180°C).
Using a hand electric mixer, beat together the egg and butter until pale yellow.
In a medium bowl, mix together the almond butter, erythritol, and egg mixture.
Sift together both flours (almond and coconut) and salt, and mix them into the batter.
Add in as much of almond meal into the dough as necessary for being able to use your hands to form a compact, 1.5 inch diameter log.
Form two logs. Wrap them tightly with plastic kitchen foil and refrigerate for 45 minutes.
Unwrap the cookie dough log, and roll it in the crushed sliced almonds, pressing down to ensure that the almonds sticks to the surface. Using a very sharp knife, cut into ¼-inch slices, and arrange on the baking pan.
Using a food processor, mix together the egg white, sliced almonds, and erythritol.
Helping yourself with a silicone brush, apply the mixture onto each cookie.
Bake the cookies for about 10 minutes. Allow them to cool slightly and move to a cooling rack.