In a large bowl, beat together the room-temperature butter, granulated sugar, and brown sugar until light and creamy, about 3–4 minutes.
Beat in the egg, egg yolk, coconut extract, and vanilla extract until just combined.
Add in the sweetened flaked coconut, salt, and cornstarch. Beat to combine. Finally, add in the flour and mix until just combined.
Lightly pack a one-tablespoon measuring spoon and level it off. This is the exact size of the dough you need! Roll that dough into a ball and place it on a parchment-paper-lined tray or plate. Cover and chill for 1 hour.
Preheat oven to 350°F. Remove from the fridge and place 1 inch apart on a parchment or silicone-lined sheet pan. Bake for 9–12 minutes or until no longer glossy on top and very lightly browned on the edges. Be careful to not overbake, as you’ll lose texture and flavor.
Remove from the oven and let cool for 1 minute. Press a 1/4-teaspoon measuring spoon into the center of each cookie. Remove cookies to a cooling rack and let cool completely.
Transfer a few tablespoons (at a time) of Nutella into a small plastic bag. Seal the bag and cut off the tip with scissors. “Pipe” the Nutella into the center of each cookie. Enjoy!
Notes
Note 1: Nutella contains hazelnuts. If you’d like to make a nut-free chocolate filling: Combine 3 tablespoons unsalted butter with 3/4 cup chocolate (dark, milk, or semi-sweet; I like milk chocolate best!) in a microwave-safe bowl. Microwave in bursts of 15 seconds, stirring between each burst for 10 seconds until melted and smooth. Use this in place of Nutella!Storage: Enjoy cookies within 1–2 days of making. Store cookies in an airtight container at room temperature.