In a large mixing bowl, beat together the butter and sugars until smooth and free of lumps. This can be done by hand or with an electric mixer. Beat in the egg, egg yolk, and vanilla until it's well incorporated.
In a small bowl, combine the flour, baking soda, cornstarch, and salt; stir with a whisk. Add to the butter mixture and stir just until combined. Gently fold in the mango, coconut, and chocolate chips.
Preheat the oven to 350ºF. Roll the dough into 1 ½ tablespoon-sized balls and place them 2 inches apart on a cookie sheet lined with parchment paper or a silicone mat. Bake for 10-12 minutes, just until the outer edges of the cookies are set. The centers will look undone. Cool the cookies on the pan for 5 minutes before transferring them to a wire rack to cool completely.
Notes
Make ahead tip
The cookies will keep for up to 1 week stored at room temperature in an airtight container.
Freeze baked cookies for up to 3 months. Thaw in the refrigerator overnight.
Freeze unbaked cookie dough balls for up to 3 months. Bring to room temperature and bake as directed.