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