Put the chocolate and butter in a saucepan and set the saucepan in a basin of simmering water. Cook, stirring occasionally, until the chocolate melts.
Combine the corn syrup and sugar and bring to the boil. Cook 2 minutes.
Put the beaten eggs in a mixing bowl. Combine the corn syrup and chocolate mixtures, and pour this over the eggs, stirring constantly. Stir in the vanilla and pecans. Turn this filling into the prepared pie plate.
Place the pie in the oven and bake45 to 50 minutes, or until the pie is well puffed. Remove and place on a rack to cool.