Just seen this and had to share, not tried it but looks good!!

For the chocolate wafers:
180g all-purpose flour
75g unsweetened Dutch process cocoa
1 tsp baking soda
1/4 tsp baking powder
1/4 tsp salt
150-225g of Sweetner - trial and error with taste, add a bit at a time!!!
110g plus 2 Tbsp unsalted light butter or margarine, room temperature
1 large egg

For the filling

110g unsalted light butter or margarin, room-temperature
450g sweetner - trial and error with taste, add a bit at a time!!!
2 tsp vanilla extract

How to make it:
1. Set two racks in the middle of the oven. Preheat to gas mark 5!
2. In a food processor or the bowl of an electric mixer, thoroughly mix the flour, cocoa, baking soda and powder, salt, and sweetner. While pulsing, or on low speed, add the butter, and then the egg.Continue processing or mixing until dough comes together in a mass.
3. Take rounded teaspoons of batter and place on a parchment paper-lined baking sheetapproximately two inches apart. With moistened hands, slightly flatten the dough. Bake for 9 minutes, rotating once for even baking. Set baking sheets on a rack to cool.
4. To make the cream, place butter in a mixing bowl, and at low speed, gradually beat in the sweetner and vanilla. Turn the mixer on high and beat for 2 to 3 minutes until filling is light and fluffy.
5. To assemble the cookies, put the cream in a pastry bag with a 1/2-inch round tip and pipe teaspoon-size blobs into the center of one cookie. I still donít have a pastry bag or tips, so I use a Ziplock bag and cut off the corner.

Not a clue what the syns come out as for these but they cant be much as it makes 25 to 30 cookies!!