01 - Preheat oven to 350°F (175°C). Line two baking sheets with parchment paper and set aside.
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 and mix until a soft, cohesive dough comes together.
04 - Scoop tablespoon-sized portions of dough and roll into smooth balls. Arrange on the prepared baking sheets, spacing them about 2 inches apart. Gently flatten each ball with your fingers or the tines of a fork for a uniform shape.
05 - Bake for 10 to 12 minutes, or until the edges are lightly golden. Remove from the oven and let the cookies cool completely on a wire rack.
06 - In a medium bowl, beat the powdered sugar and softened vegan butter together until light and fluffy. Add the lemon juice, lemon zest, and turmeric if using, then continue beating until the filling is smooth and creamy.
07 - Pipe or spread a small dollop of lemon filling onto the flat side of half the cooled cookies. Gently press the remaining cookies on top, flat side down, to form neat sandwiches.
08 - Refrigerate the assembled cookies for at least 30 minutes to allow the filling to set and achieve the best texture before serving.