Preheat oven to 350 degrees F. Line two baking sheets with parchment paper. Set aside.
In a large mixing bowl, mix all purpose flour, baking soda, baking powder and salt.
In a separate bowl, whisk melted butter, 1 ¾ cups of coconut sugar, egg, egg yolk, and vanilla extract until fully combined and no lumps remain.
Pour the wet ingredients into the dry ingredients. Using a spatula, stir to ensure no flour pockets remain and ingredients are evenly distributed. At first, you might feel like there is not enough liuid to the amount of flour, but the recipe is correct.
Place the reserved ¼ cup coconut sugar on a plate. Divide dough into 24 portions, each about 2 tablespoons, rolling between hands into balls. Working in batches, gently roll each cookie ball in the coconut sugar making sure each ball is coated with the sugar.
Place coconut sugar cookies on the prepared baking sheet, spacing them about 2 inches apart, 12 dough balls per sheet. Using the back of a glass or a ramekin, lightly press on each cookie to slightly flatten.
Bake one sheet at a time until cookies are browned and edges have begun to set but centers are still soft , 12 to 14 minutes, rotating baking sheet halfway through baking. When they first come out of the oven they will look like they are underbaked. This is normal. Resist the temptation to bake them longer.
Cool cookies on a baking sheet for 5 minutes. Using a metal spatula, transfer cookies to a wire rack and cool to room temperature.