Preheat the oven to 180°C (350°F), Gas Mark 4, and put a baking sheet in the oven to heat through. Melt the chocolate in a bowl over a pan of simmering water (see
Heat the sugar and maple syrup in a pan gently until the sugar dissolves. Leave to cool slightly. Lightly whisk the eggs to a smooth consistency. Whisk in both the chocolate and the syrup mixtures.
Grease a loose-based flan tin, 23 cm (9 inches) in diameter and 3 cm (1¼ inches) deep. Roll out the pastry on a lightly floured surface and use to line the tin. Pour the filling into the pastry case. Place on the hot baking sheet in the oven and bake for 15 minutes until the filling is just beginning to set.
Remove the tart from the oven and scatter the pecan nuts over the top. Bake for a further 10 minutes until the nuts are beginning to brown. Remove from the oven and raise the temperature to 230°C (450°F), Gas Mark 8. Dust the tart generously with icing sugar and return to the oven for about 5 minutes until the nuts are beginning to caramelize. Leave to cool for 20 minutes before serving.