A huge thank you to the italianrecipebook.com.  I never would  have thought that hard-boiled egg yolks would be used in any cookie.  This is phenomenal.

Ingredients:

4 hard-boiled eggs with yolks separated. (recipe here)
7 oz All Purpose Flour; 200 g
1 cup cornstarch + 1 tsp; 130 g
7 oz cold butter; 200 g
⅔ cup confectioners sugar; 100 g
1 lemon , zest only
1 tsp vanilla extract

 

Instructions:

1.  Boil the eggs.  Peel eggs and separate the yolks.   This step can be done well in advance.
2.  Sift flour, cornstarch and confectioners sugar in a large bowl. Add lemon zest, vanilla (optional) and cold butter cut in cubes. Chop everything with dough blender or in a food processor.
3.   Add grated egg yolks and knead the dough by hand until it comes together in a smooth ball.
4.    Cover with a plastic wrap and set aside to rest for about 30-60 minutes.
5.    You can also place it in the fridge overnight but remember to take it out at least 1-2 hours before you start to make cookies.
6.  Preheat oven to 335F (170C).
7.  Cut off a large piece of the dough. On a lightly floured work surface roll it out ⅓ inch thick.
8. Using a cookie cutter, cut out the cookies.
9. Transfer cookies on a baking sheet lined with parchment paper and bake in preheated oven for 10-15 minutes. Canestrelli should remain pale and should not get brown.
10.  Let cookies cool completely on a wire rack and generously dust with confectioners sugar.