(Yields about 55-60 cookies)

1-1/2 cups (200 g) all purpose flour, unbleached + extra to roll the dough
3/4 cup (100 g) potato starch or cornstarch
1 pinch of salt
14 tbsp (200 g) unsalted butter
1/2 cup (100 g) sugar (confectioners' is best but regular will do)
5 hard-boiled yolks
1 tsp pure vanilla extract (I like to add grated lemon and/or orange zest instead)
confectioners’ sugar
Optional: apricot jam (about half a jar) and honey (about 2-3 Tbsps) to fill

Place the flour and starch in the bowl of a food processor and pulse until well mixed. Add the butter, diced, and pulse until the mixture looks like wet sand. Add the sugar and pulse until well incorporated. Add the yolks, and pulse until they are crumbled. Add the vanilla extract (or lemon and/or orange zest), and pulse until the dough forms (it might take a few seconds, and it might look like the mixture is too dry, but if the machine keeps working the dough will eventually form. Gather the dough in a piece of wax paper or plastic wrap and leave to rest in a cool place (not the refrigerator).
Preheat the oven to 325°F (160°C)
Sprinkle a little flour on the work surface and roll the dough to a scant 1/4-inch (5 mm) thickness. With a cookie cutter cut the cookies (the traditional shape is a ring, which can be made with a donut cutter). Place the cookies on a baking sheet lined with parchment paper. If you want to fill them (after baking) -which is what I do - instead of making rings, roll out some thin logs, cut in pieces and roll into small balls. I then push my finger to make an indentation (just like making thumbprint cookies).
Bake for about 10-12 minutes, taking care that the cookies do not darken. (If you made the small balls with indentation, at the 8 minute mark, check to see that they are still there. If they are not pull the tray out and make indentations again).
Let the cookies cool on a rack. They are extremely fragile while hot, and they will literally disintegrate if removed from the pans while hot.
Once the cookies are cool sprinkle with confectioners’ sugar. If you made the balls, now is the time to fill the indentations with with a mixture of jam and honey. Store in airtight containers.

Note: to hard-boil bring a small pot of water to boil, then gently place eggs in the water (using a spoon) and allow to boil for 10 minutes. Turn off, rinse in cold water and peel. Cut in half and remove the yolks for the recipe. Keep the whites for something else (they make a great snack if lightly sprinkled with salt).

(The recipe is adapted from the original recipe by Giuseppe Ciocca in: “Il Pasticcere e Confettiere Moderno”, 1907—Italy)