Sift the flour, salt, corn starch, and baking soda together then whisk together and set aside.
Beat butter and sugars in a stand mixer fitted with a paddle attachment until light and fluffy. Mix in the egg, and vanilla extract. Scrape the bowl down and mix once more.
Add the dry mixture to the wet and beat until almost combined. Scrape the bowl down one last time then add the toasted coconut and mix on low until just combined. Use a spatula to finish incorporating any stray bits of coconut that haven't mixed In yet.
Cover and shill the dough for at least 30 minutes. You can chill it overnight or make the dough months ahead of time and freeze it.
Once chilled set oven to 350F and scoop out potions of cookie dough roughly two tablespoons in size (a little larger is fine too. Place the dough onto parchment-lined baking sheets leaving about two inches of space between the cookies to allow for spreading.
Bake at 350F for about 10 minutes or until the edges are set, you don't want these cookies to over-bake but the bottom of the edge will be golden and set.
Measure your flour correctly! Adding too much flour to the recipe is the most common mistake. The best, and easiest way to measure flour is by using a scale. If you don't have one then fluff your flour with a spoon, sprinkle it into your measuring cup, and use a knife to level it off.
Chill time is very important for these cookies so try not to rush things.
You can make a simple glaze with coconut milk and powdered sugar for an extra layer of sweetness if desired. Just mix up and drizzle on when cool.
These cookies will keep for up to a week in a sealed container.