Preheat the oven to 325°F. In a large saucepan, melt the butter over medium heat. Once the butter has melted, remove it from the heat and add the sugar. Stir until the sugar is well incorporated and mostly smooth. Let cool for a few minutes.
While the mixture is cooling, mix together the dry ingredients and set aside. Whisk together the egg, egg yolk and vanilla, and then add to the sugar and butter mixture.
Slowly add the dry ingredients in three stages and stir to combine. COOL COMPLETELY before adding the chocolate chips and coconut. Stir well to make sure the chocolate chips and coconut are evenly distributed.
Scoop the dough onto a parchment-lined baking sheet and roll it into balls with your hands. Press down lightly to flatten each one before baking.
Bake for 10-12 minutes. Let cool for 1-2 minutes on the baking sheet and then remove to a wire rack.