Preparation Steps

• Preheat oven to 350°F. Line 2 baking sheets with parchment paper.
• Whisk flour, baking powder, baking soda, and salt in a bowl; set aside.
• In a large bowl, beat 1 cup softened butter and granulated sugar until light and fluffy, about 2 to 3 minutes.
• Beat in egg, sour cream, vanilla, lemon zest, and lemon juice until smooth.
• Add dry ingredients to wet and mix on low just until combined. Do not overmix.
• Scoop dough into 1.5 tablespoon mounds onto prepared sheets, spacing about 2 inches apart. Gently flatten tops slightly.
• Bake 8 to 10 minutes, until edges look set and tops remain pale. Cool on the sheet 5 minutes, then transfer to a rack to cool completely.
• For the frosting: Beat 0.5 cup softened butter until creamy. Gradually mix in powdered sugar, then lemon juice, vanilla, cream, zest, and salt until smooth and spreadable.
• Frost cooled cookies generously. Let frosting set for about 20 minutes before serving.
• Store cookies in an airtight container at room temperature for 2 days or refrigerate up to 5 days.