• In a large bowl, beat together the butter and sugar until well combined. Add the lemon juice and zest, and mix to combine.
• In a separate small bowl, whisk the flour and cornstarch together. Gradually mix the flour mixture into the butter mixture until a dough forms.
• Divide the dough in half and shape each half into a log (about 6 inches long). Wrap each log in plastic wrap and refrigerate for at least 2 hours, or until firm.
• Preheat your oven to 350°F. While the oven is heating, unwrap the dough and slice it crosswise into ¼-inch-thick rounds. Place the slices 2 inches apart on ungreased baking sheets.
• Bake the cookies for 10 to 12 minutes, or until firm. Remove them from the baking sheets and transfer to wire racks to cool completely.

Lemon Frosting (optional)

• In a mixing bowl, beat the softened butter until smooth and creamy. Gradually add the confectioners' sugar while continuing to beat. Add the lemon juice and zest. Beat until the mixture is smooth and creamy, adjusting the consistency with more sugar or lemon juice if necessary. Mix in food coloring, if using.