Preheat the oven to 180 degrees C. Line a baking tray with baking paper.
In a medium bowl, mix together the ground walnuts, 3 egg yolks, sugar, cardamom, bicarb soda and rose water until well blended.
Roll teaspoon sized pieces of dough into balls then place onto the baking paper lined baking trays. Cookies should be spaced 5cm apart.
Whisk together the remaining egg yolk and water using a fork. Press a walnut piece into each cookie, then brush with the egg yolk glaze.
Bake for 20 minutes in the preheated oven or until golden. The cookies will appear soft and undercooked but they will harden when cooled. Allow them to cool on the baking trays for at least 10 minutes before transferring to a wire rack to cool completely.