Preheat your oven to 325°F (160°C) and prepare two baking sheets by lining them with parchment paper or silicone mats.
In a food processor, combine the almond flour, powdered sweetener, and salt. Pulse briefly to ensure they are well mixed.
Cut the softened butter into small chunks and add them to the food processor. Pulse again until the mixture resembles coarse crumbs.
Introduce the egg and vanilla extract to the processor. Continue to process until the dough comes together and forms a cohesive ball.
Fit a piping bag with a large open star tip (such as an Ateco #824) and fill it with the cookie dough. Holding the bag straight up, pipe the dough into tight circles, about 2 inches in diameter, onto your prepared baking sheets. Don't worry if they're not perfect; you can always scoop up any mistakes and re-pipe them!
Bake the cookies for about 18 to 20 minutes, or until you notice the edges turning lightly golden brown.
Carefully remove the cookies from the oven and turn the oven off. Let the oven cool down for about 15 minutes, then return the cookies to the warm, turned-off oven for an additional 15 to 20 minutes. This step helps them dry out and become perfectly crisp without over-browning.
Take them out and allow them to cool completely on a wire rack before handling.
If you wish to decorate, gently melt the chopped sugar-free dark chocolate and cocoa butter (or coconut oil) in a heatproof bowl set over a pot of barely simmering water, stirring until smooth.
Dip half of each cooled cookie into the melted chocolate. Place them on a wax paper-lined sheet and sprinkle with sugar-free sprinkles if desired. Let the chocolate set completely before serving.