This is a mini version of the famous cake from Brittany. Keep in mind that your pastry does not need to come out as perfect as store bought puff pastry. In the worst case, if the turning fails, you can just put it in a cake tin and bake it - it will still taste good.
Fleur de sel, aka fleur de sel de Guerande, is sold at specialty stores and online.
You can also cut the dough into long strips instead of squares and roll them up like a snail, then rise and bake as described.