Beat the softened butter, egg, monk fruit sweetener and vanilla using an electric mixer until lightly whipped.
Add in almond flour 1/2 cup at a time stirring with a spatula to blend the flour in.
Add tapioca starch and salt stirring with a spatula to blend in. Use clean hands to mix ingredients in the dough if that's easier.
Form the cookie dough in a log shape. Wrap the log rather tightly with plastic wrap to keep form. Chill it for 30-45 minutes in the freezer. If time allows, chill the log in the fridge overnight.
Once ready to bake, preheat oven to 350 F. Line a large baking sheet with parchment paper.
Using a very sharp knife, slice log in 1.25 cm circles, placing each cookie on the sheet about 4 cm apart.
Bake for 15-20 minutes. Edges should be light golden brown.
Allow cookies to cool on baking sheet at least 5 minutes. Transfer to cooling rack.