• lemon zest (from one whole lemon)
• 2/3 cup unsalted butter (softened)
• 2 tablespoons fresh lemon juice
• 1 teaspoon pure vanilla extract
• 2 cups all-purpose flour
• 2 teaspoons baking powder
• 1 1/4 cups confectioners' sugar (sifted)
• 1 tablespoon fresh lemon juice
• sparkling sugar for sprinkling (optional)