1. Preheat the oven to 350°F (175°C) and line a baking sheet with parchment paper. In a medium mixing bowl, combine the flour and powdered sugar. Add the cold butter and blend until the mixture resembles coarse crumbs.

2. Roll the dough into balls about 1 inch in diameter. Flatten each gently with your palm and place on the baking sheet. Bake for 10–12 minutes until edges are lightly golden. Cool completely on a wire rack.

3. In a medium bowl, whisk together the eggs and sugar until smooth. Add flour, baking powder, lemon juice, shredded coconut, and vanilla extract if using. Stir until well combined.

4. Pour the mixture into a saucepan and cook over medium heat, stirring constantly, until it thickens into a smooth custard. Remove from heat and let cool completely.

5. Spoon the cooled filling onto the flat side of one cookie, then top with another cookie to create a sandwich. Sprinkle the tops with extra shredded coconut.