To make the cupcakes: Preheat your oven to 350ºF (175ºC) and line 36 muffin cups with cupcake liners. In a medium bowl, whisk together the flour, baking powder, and salt; set aside. In a large bowl, use an electric mixer on medium speed to beat the sugar and softened butter until creamy. Add the eggs one at a time, beating well after each addition. Mix in the coconut and vanilla extracts. With the mixer on low speed, gradually add the flour mixture and buttermilk alternately in three parts: start with one-third of the flour mixture, then half of the buttermilk, followed by another third of the flour, the remaining buttermilk, and finally the rest of the flour. Beat just until combined to avoid overmixing. Divide the batter evenly among the muffin cups, filling each about two-thirds full. Bake for 15 to 18 minutes, or until a toothpick inserted into the center comes out clean. Let the cupcakes cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.

To prepare the lemon curd: In a medium saucepan, combine the sugar, cornstarch, and salt. Add the water, slightly beaten egg yolks, and lemon juice, stirring to blend. Cook over medium heat, stirring frequently, until the mixture thickens. Remove from heat, then stir in the butter and lemon zest. Pour the curd into a bowl, cover, and refrigerate until fully chilled.

To make the fluffy frosting: Using a stand mixer, beat the egg whites until stiff peaks form. While the egg whites whip, heat the sugar and light corn syrup in a saucepan over medium heat until it reaches a full boil, then remove from heat. With the mixer running, slowly drizzle the hot sugar syrup into the whipped egg whites without scraping the sides of the bowl to prevent sugar crystallization. Continue beating for 5 to 7 minutes, until the frosting is glossy and fluffy. Beat in the vanilla extract.

To assemble the cupcakes: Using a sharp knife, cut a cone-shaped piece out of the center of each cupcake, keeping the removed piece. Spoon about 1 teaspoon of lemon curd into the hollowed center, then replace the cut-out piece on top. Repeat with all cupcakes. Pipe the fluffy frosting over each cupcake and finish by sprinkling sweetened flaked coconut on top.