To make the pastry, mix together the sugar, eggs (yolks?) and butter in a large bowl. Sift the flour onto the buttery mixture and, using your fingers, rub it all together until you get a sandy texture. Add the water and quickly press it into soft dough. Wrap the dough in cling film and refrigerate for a minimum of four hours.
Melt the chocolate and the butter together in a bowl over simmering water, set aside. In a medium sized saucepan, combine the sugar and syrup and bring to the boil, stirring constantly. Set aside to cool.
Beat the eggs in a large bowl, then stir in the melted chocolate-butter mixture and whisk in the sugar syrup mixture so that it is all thouroughly combined. Add the vanilla extract and stir in the pecans. Set aside until completely cool.
Pour the filling into the chilled pastry and bake in the oven at 200 degrees Celcius, for 20 minutes, then lower the temperature to 180 degrees Celcius and continue to cook for about 20 minutes until the pastry is golden and the filling is set.