01 - Preheat the oven to 350°F. Line two baking trays 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. Place on the prepared baking trays, spacing them about 2 inches apart. Flatten each ball gently with your fingers or a fork for a uniform, even shape.
05 - Bake for 10 to 12 minutes, 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 vegan butter together with an electric mixer until light and fluffy. Add the lemon juice, lemon zest, and turmeric if using, then beat until smooth and creamy.
07 - Pipe or spread a small amount of filling onto the flat side of half the cooled cookies. Press the remaining cookies on top, flat side down, to form sandwiches.
08 - Refrigerate the assembled cookies for 30 minutes to allow the filling to set and achieve the best texture before serving.