Step 1: Preheat your oven to 350°F (175°C) and line two large baking sheets with parchment paper or silicone mats.
Step 2: In a large bowl, cream together the softened butter and 1/2 cup of powdered sugar until light and fluffy, about 3 minutes.
Step 3: Add the lemon zest and lemon juice to the butter mixture and beat until well combined.
Step 4: In a separate bowl, whisk together the flour, cornstarch, and salt.
Step 5: Gradually add the dry ingredients to the wet ingredients, mixing on low speed just until a soft dough forms. Do not overmix.
Step 6: Scoop rounded tablespoons of dough and roll them into small balls. Place them on the prepared baking sheets about 2 inches apart.
Step 7: Bake for 10-12 minutes, or until the bottoms are barely golden brown. The tops should remain pale.
Step 8: Let the cookies cool on the baking sheet for 5 minutes, then gently roll them in extra powdered sugar while still warm.
Step 9: Transfer to a wire rack to cool completely, then roll in powdered sugar once more if desired for a snowy finish.