In a large mixing bowl, combine unsalted butter and powdered sugar. Beat until light and fluffy, about 2-3 minutes.

Mix in lemon zest, lemon juice, and vanilla extract. Beat until well combined.

Whisk together flour, cornstarch, and salt in a separate bowl. Gradually mix into wet ingredients until a soft dough forms.

Divide the dough into logs, wrap in plastic wrap, and refrigerate for at least 1 hour.

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

Slice the dough logs into 1/4-inch rounds and place on baking sheets. Bake for 10-12 minutes until edges are golden.

Cool cookies on sheets, then toss in powdered sugar to coat while warm.