Place all of the well-scrubbed potatoes in a 3 litre saucepan. Cover with cold water and bring to a boil over high heat. Reduce heat to a simmer and cook until potatoes are very soft, about 20-30 minutes. Drain and when cool enough to handle, peel. In medium bowl, combine potatoes, butter, brown sugar and nutmeg. Using a potato masher, cream the potatotes until very smooth. In small bowl, beat eggs, 1 cup evaporated milk and vanilla together. Beat this mixture into the potatoes. Mix thoroughly. Pour into piecrust and drizzle the remaining quarter cup of milk on top. Bake 15 minutes in a preheated 230ºC oven then turn heat to 160ºC and continue baking for 30 minutes or more until the filling is set.