Sift together the flour and salt in a large bowl and set aside.
Beat the butter with electric beaters until light and fluffy. Add Natvia and beat until combined.
Add the egg yolk and vanilla and continue beating.
Add the flour and Fangks and mix until just combined.
Add chocolate chip pieces and mix by hand to make sure they're evenly distributed in the mixture.
Roll the dough out on a lightly floured surface. (might need to do this in two batches.) Put the dough in the fridge for at least 30 minutes to firm up.
Cut shapes out of the dough and place on a lined baking sheet. Bake for about 10-12 minutes until they're just golden brown around the edges. Allow to cool a little on the tray before moving to a cooling rack and allowing them to cool completely.