01 - Preheat oven to 350°F and line two baking trays 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 the softened vegan butter, melted coconut oil, vanilla extract, and lemon zest to the dry mixture. Stir until a soft, cohesive dough comes together.
04 - Scoop tablespoon-sized portions of dough and roll into balls. Place on the prepared trays, spacing them about 2 inches apart. Flatten each ball gently with your fingers or a fork for a uniform shape.
05 - Bake for 10 to 12 minutes, until the edges are lightly golden. Transfer to a wire rack and cool completely.
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 beat until creamy and smooth.
07 - Pipe or spread a small dollop of filling onto the flat side of half the cooled cookies. Top each with a second cookie, flat side down, pressing gently to form a sandwich.
08 - Refrigerate the assembled cookies for at least 30 minutes to firm the filling before serving.