Preheat oven to 350°F (175°C). Line a baking sheet with parchment paper.

In a bowl, mix 1 cup flour with ¼ cup powdered sugar. Cut in cold butter until the mixture resembles coarse crumbs.

Form dough into 1-inch balls, flatten slightly, and place on baking sheet.

Bake for 10–12 minutes, or until edges are lightly golden. Let cookies cool completely on a wire rack.

Prepare the filling: In a medium bowl, whisk eggs and sugar until smooth. Add flour, baking powder, lemon juice, shredded coconut, and vanilla (if using). Stir to combine.

Transfer mixture to a saucepan and cook over medium heat, stirring constantly, until thickened to a custard-like consistency (about 5–10 minutes). Let cool completely.

Once both cookies and filling are cooled, spoon a dollop of lemon-coconut filling onto the flat side of one cookie, then top with another to make a sandwich.

Sprinkle extra shredded coconut on top of the assembled sandwiches.

Serve immediately or refrigerate to firm up the filling.