Use a kitchen robot to beat the butter and fondant into a cream. Add the vanilla at appropriate times.
Spray a few dots of chocolate on the 2 5mm slats and place the other slats on top.
Spread the cream between the 2 slats.
Use a cutting roller to make a "dash" every 22mm. (So definitely don't cut it!!)
Place 3 hazelnuts on each piece
Let set for 15 min in the refrigerator.
Cut the pieces with a large knife. Use the "dashes" as a guide.
Let the loose pieces stiffen in the refrigerator for 15 min.