In a bowl, beat together the butter and sweetener for 1 minute. Then add egg, almond and vanilla extract. Beat to combine.
Add in the coconut and almond flours, salt and Xantan gum, beat until just combined.
Form a ball and press to form a disk, wrap in plastic wrap. Chill for at least 1 hour or overnight.
Roll out the dough between parchment paper into a 1/8-inch thickness. Cut equal amount of rounds, using the cutter without the insert and with the insert. Transfer to a parchment paper lined baking sheet. Refrigerate for 15-30 minutes.
Preheat oven to 350 F. Bake cookies for 10-12 minutes, until the edges are golden. Cool cookies for 10 minutes on the baking sheet, then transfer to a cooling rack.
Dust the top parts with powdered low-carb sweetener. Then add about 1/2 tsp of sugar-free jam to the bottom of halves and sandwich together with the tops.