In a medium bowl, whisk the flour with the coconut, baking soda and salt. In a standing electric mixer fitted with a paddle, or using a hand mixer in a large bowl, beat the butter with the sugar at medium speed until light and fluffy, about 3 minutes. Beat in the egg yolk and vanilla, scraping the side and bottom of the bowl. Beat in the dry ingredients at medium-low speed. Wrap the dough in plastic and refrigerate for 15 minutes.