Heat your milk in a small pot at low-medium heat so it's hot, but not boiling.

In a double boiler over hot water, combine the brown sugar, flour and butter. Stir until blended.

Add the milk to the double boiler., and mix.

Beat your egg yolks in a bowl until they are lighter in colour.

Spoon some of the sugar/milk mixture into the eggs, stirring well after each spoonful. You are bringing the temperature of the eggs up so they won't immediately cook when you add them to the mixture and end up with floating scrambled eggs. That would be gross.

Add the eggs to the double boiler and cook again, stirring the mixture until it's thickened, about 3-5 minutes.

Remove from the heat, and let cool for 5-10 minutes.

Preheat the oven to 325°F.

Stir in the vanilla, and then pour into the baked pie shell. If you want to cover it with meringue, do that now.

Bake for 40-45 minutes, or until browned and an inserted toothpick comes out clean.

Serve with whipped cream!