01 - Preheat oven to 350°F and line two baking sheets with parchment paper.
02 - In a large mixing bowl, whisk together the all-purpose flour, powdered sugar, cornstarch, and salt until evenly blended.
03 - Add softened vegan butter, melted coconut oil, vanilla extract, and lemon zest to the dry mixture. Stir until a soft, cohesive dough forms.
04 - Scoop tablespoon-sized portions of dough and roll into balls. Arrange on prepared baking sheets, spacing them 2 inches apart. Flatten each ball gently with your fingers or a fork for uniform thickness.
05 - Bake for 10 to 12 minutes until edges are lightly golden. Transfer cookies to a wire rack and cool completely.
06 - Beat powdered sugar and softened vegan butter together with an electric mixer until light and fluffy. Add lemon juice, lemon zest, and turmeric if using. Beat until smooth and creamy.
07 - Pipe or spread a small amount of filling onto the flat side of half the cookies. Top each with a second cookie, flat side down, to form sandwiches.
08 - Refrigerate assembled cookies for 30 minutes to firm the filling before serving for the best texture.