Fill the lower pot of a double boiler with water.

Place the milk in the upper pot of the double boiler.

Heat the milk over medium heat until warmed through.

In a separate bowl, beat the eggs until light and frothy.

Add the sugar to the beaten eggs and mix well.

Gradually pour a small amount of the warm milk into the egg mixture, whisking constantly to temper the eggs.

Slowly pour the tempered egg mixture into the remaining warm milk in the double boiler.

Cook over medium heat, stirring constantly, until the custard thickens enough to coat the back of a spoon.

Be careful not to overcook the custard.

Remove from heat and stir in the vanilla extract.

Transfer the custard to a serving dish or individual cups.

Chill in the refrigerator until completely cold before serving.