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 distributed.
03 - Add the 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 the prepared baking sheets, spacing them 2 inches apart.
05 - Gently press each dough ball with your fingers or the tines of a fork to create a uniform, flat shape.
06 - Bake for 10 to 12 minutes, or 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 continue beating until creamy and smooth.
08 - Pipe or spread a small dollop of filling onto the flat side of half the cookies. Press the remaining cookies on top, flat side down, to form sandwiches.
09 - Refrigerate the assembled cookies for 30 minutes to firm up the filling before serving.