In a medium bowl, whisk together all-purpose flour, cornstarch, and fine sea salt until thoroughly blended. Set aside.

In a stand mixer fitted with the paddle or whisk attachment, beat the softened butter and sifted powdered sugar on low speed until combined, then increase to medium-high speed and beat continuously for strictly 8 to 10 minutes, scraping down the bowl halfway through. The butter will turn exceptionally pale, snowy white, and fluffy like whipped frosting!

Beat in the vanilla extract until fully incorporated.

Turn the mixer to the lowest speed and gradually add the flour and cornstarch mixture in three parts, mixing just until the flour disappears and a soft, pillowy dough forms. Do not overmix.

Preheat your oven to 325°F (165°C) and line two large baking sheets with parchment paper.

Transfer the soft dough into a heavy-duty piping bag fitted with a large open star tip (such as Wilton 1M). Pipe 1.5-inch fluted rosettes 1.5 inches apart on the baking sheets. (Alternatively, drop 1-tablespoon scoops and gently indent with a fork dusted in flour).

Gently press half of a candied red cherry into the center of each rosette and sprinkle lightly with sanding sugar.

Bake at 325°F for 14 to 17 minutes until the cookies are set and dry to the touch, and the undersides are just faintly pale golden, but the tops remain pristine ivory white. Do not let the tops brown!

Allow cookies to cool completely on the baking sheet for 10 minutes before moving; they are extremely delicate while warm. Transfer carefully to a wire rack to cool completely.