Hard‑boil eggs, cool, peel, discard whites and mash yolks finely with a fork.

In a food processor, pulse flour, powdered sugar, salt, cornstarch and lemon zest until combined.

Add cold butter and vanilla; pulse until mixture resembles coarse crumbs.

Add mashed egg yolks; pulse just until dough comes together. Transfer to a lightly floured surface, knead gently into a smooth ball.

Wrap dough and chill for 1–2 hours or overnight until firm.

Preheat oven to 170 °C (335 °F). Line baking sheets with parchment.

Roll dough to ~1 cm thickness on floured surface. Cut with a flower‑shaped cutter; use a small round cutter or straw to punch the center hole.

Bake for 12‑14 minutes, just until set—not browned. Let cookies rest 5 minutes on baking sheet, then transfer to wire rack to cool completely.

Dust generously with powdered sugar before serving.