3 eggs (or 4 eggs for less sweet version)
Beat eggs slightly with a fork and add sugar and flour and mix with a wooden spoon. Then add melted butter and mix well. Add buttermilk and vanilla and mix. Add a dash of nutmeg if you are so inclined.
Dust the unbaked pie shell with a little bit of flour. Pour batter into shell, and then sprinkle a little more flour on top. (oops I did not do that and it turned out fine)
Bake at 325 degrees until the custard is set, approximately 1 hour. The custard will shake a little but if you push a butter knife in the middle it will come out clean. Also, there will be a nice bit of browning on top. I let the pie cool slightly and then had a slice. Then I covered and chilled it for the coworkers the next day.