01 - Cream softened butter and powdered sugar in large bowl until light and fluffy using electric mixer.
02 - Beat in lemon juice, lemon zest, and vanilla extract until fully incorporated.
03 - Mix in salt, flour, and cornstarch until soft dough forms.
04 - Divide dough in half, roll each portion into 1-inch diameter logs, wrap in plastic, and refrigerate 30 minutes.
05 - Set oven to 350°F. Line two baking sheets with parchment paper.
06 - Unwrap dough, cut into 1/4-inch rounds, and place on prepared baking sheets 1 inch apart.
07 - Bake 10-12 minutes until edges are barely golden.
08 - Let cool 5 minutes on baking sheets, then toss in powdered sugar while warm.
09 - Transfer to wire rack to cool completely. Dust with extra powdered sugar before serving.