Step 1: Make the Lemon Curd (if making homemade)

1. In a medium heatproof bowl, whisk together the egg yolks, sugar, lemon juice, and lemon zest until smooth.
2. Place the bowl over a saucepan of simmering water (double boiler) and cook the mixture, stirring constantly with a silicone spatula, for 8-10 minutes or until it thickens enough to coat the back of a spoon.
3. Remove from heat and whisk in the butter, one piece at a time, until fully incorporated and smooth.
4. Strain the lemon curd through a fine mesh sieve to remove any cooked egg bits. Transfer to a clean container, cover with plastic wrap pressed against the surface, and refrigerate until set (about 1 hour).

Step 2: Prepare the Cookie Dough

1. In a large mixing bowl, cream the softened butter, granulated sugar, and powdered sugar using an electric mixer on medium speed until light and fluffy (about 2 minutes).
2. Add the egg yolk and vanilla extract, beating until fully combined.
3. Gradually mix in the flour, shredded coconut, and salt until a soft dough forms. Avoid overmixing to keep the cookies tender.
4. Wrap the dough in plastic wrap and refrigerate for at least 30 minutes to make it easier to handle.

Step 3: Shape and Bake the Cookies

1. Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper or a silicone baking mat.
2. Roll the chilled dough into 1-inch balls and place them about 2 inches apart on the prepared baking sheet.
3. Use your thumb or the back of a spoon to gently press an indentation into the center of each dough ball. If the dough cracks slightly, smooth the edges with your fingers.
4. Bake the cookies for 10-12 minutes, or until the edges are just starting to turn golden. Do not overbake, as they will continue to set as they cool.

Step 4: Fill and Garnish the Cookies

1. Let the cookies cool on the baking sheet for 5 minutes, then transfer them to a wire rack to cool completely.
2. Once cooled, fill each indentation with a spoonful of lemon curd. For a neater presentation, use a piping bag or zip-top bag with the corner snipped off to pipe the curd into the centers.
3. Sprinkle the cookies with extra shredded coconut (toasted if preferred) or a dusting of powdered sugar for garnish.