Preheat the oven to 400 degrees F. Dock the pastry shell all over with the tines of a fork. This will keep it from buckling. Bake for 10 minutes.
Meanwhile, combine the eggs, milk, sugar, vanilla, and nutmeg. Whisk in the flour until well blended. If the flour doesn't want to blend in, pour it into a blender to whip it all together. That should do it.
Set the pie plate on a tray. This is solely for the purposes of transport, since custard filling is very liquid and runny. Pour the egg mixture into the baked pie shell and move the whole tray over to the stove top. Open the oven and very carefully transfer the pie plate to the oven rack.
Bake at 400 degrees F for 10 minutes, reduce heat to 325 degrees F and bake an additional 20 to 30 minutes or until a knife inserted into the center comes out clean.
Cool to room temperature before serving. Store leftovers in refrigerator.