Begin by placing softened unsalted butter in a mixing bowl. Beat the butter with ½ cup of powdered sugar using an electric mixer on medium speed until light and fluffy, about 2-3 minutes.

Lower the mixer speed and incorporate the fresh lemon zest, lemon juice, and vanilla extract into the butter-sugar mixture. Mix until thoroughly combined, about 1 minute.

In a separate bowl, whisk together 1 cup of all-purpose flour, ½ cup of cornstarch, and a pinch of salt. Ensure there are no lumps in the mixture.

Gradually add the dry ingredient mixture to the wet mixture, gently folding together with a spatula until a soft dough forms.

Shape the dough into two logs, about 1.5 inches in diameter. Wrap each log in plastic wrap and refrigerate for at least 1 hour.

Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper.

Once firm, slice the dough into ¼-inch thick rounds and place them on the baking sheets, spacing them about 1 inch apart.

Bake for 10-12 minutes, watching for slightly golden edges while keeping the centers pale.

Remove from the oven and let cool on baking sheets for about 5 minutes before transferring to a cooling rack.

While warm, dust generously with powdered sugar, then let cool completely and dust again.