Preheat the oven to 350 degrees F and line a baking sheet with parchment paper. Place the brioche buns on the baking sheet without separating them.
To a medium bowl, add the coconut, sugar, milk, melted butter, whole egg, egg yolk, vanilla, and kosher salt. Mix with a spoon until creamy and smooth.
Spread the coconut mixture evenly over the buns to cover.
Bake for 12-13 minutes, or until the coconut is slightly golden.
Cool for 15 minutes. Then dust with powdered sugar before serving.