Put the hazelnut butter in a bowl; melt in the microwave dark chocolate broken into cubes together with maple syrup. Add the chocolate mixture to the bowl; add vanilla extract and a pinch of salt, and mix well.
Spread the filling on the dough, leaving a narrow margin around.
Roll the dough - use the technique for rolling sushi with the paper under the dough (see image). You can brush the roll with maple syrup for extra shine and sweetness, but it's not mandatory.
Cut into slices of 1cm (0.4-Inch) using a Serrated knife. Place them on a baking tray lined with baking paper.
Bake for 15-20 minutes until nicely golden. Take out, and cool to room temperature. The snails keep in an airtight container for at least a week.