Preheat oven to 350°F.
In a small saucepan, combine sugar and flour. Whisk in evaporated milk and egg yolks until smooth. Turn the pan to medium heat.
Stirring constantly, add milk. Once the sugar dissolves, add butter and continue stirring.
Cook until mixture thickens and comes to a gentle boil. The mixture will appear to bubble or burp. This should take about 5-7 minutes.
Turn off the heat and carefully fold 1/2 cup coconut into the hot filling.
Divide the filling equally into the pre-baked pie shells.
Quickly spread the meringue over the hot pie filling. Spread the meringue to the edge of the pie pastry to seal it and prevent it from shrinking as it bakes (see below). Use a spoon to swirl and twist the meringue as you spread it.
Evenly sprinkle the remaining coconut on top of both pies.
Bake 15-17 minutes, or until the meringue is golden brown on top.