Preheat the oven to 350 degrees F. In the bowl of an electric mixer and using the whisk attachment, beat the eggs, coconut, sugar, buttermilk, butter, flour and vanilla until well combined. Your mixture may look curdled but keep beating on high until it comes together (it will still be chunky from the coconut).
Pour the filling into the pie shell. Bake until lightly browned, the center of the pie doesn't jiggle when shaken lightly and a toothpick inserted into the center comes out moist but not covered with custard, 45 to 50 minutes. The coconut will rise to form a top crust during baking. Set the pie on a wire rack and cool completely before serving, about 1 hour.
Adapted from "Georgia Cooking in an Oklahoma Kitchen" by Trisha Yearwood © Clarkson Potter 2008. Provided courtesy of Trisha Yearwood. All rights reserved.