Break 3 1/2 oz (100 g/3 1/2 oz) of chocolate into pieces and melt in a bowl in the microwave oven for 1 minute on HIGH.
Stir.
Heat the milk in a bowl for 4 minutes on HIGH.
Put the whole egg, 2 egg yolks and 31/2 oz (100 g/31/2 oz) of sugar in a large bowl and whisk, gradually adding the cornstarch (cornflour).
Pour the hot milk over the melted chocolate and stir well.
Pour this mixture in a thin stream over the eggs, whisking constantly.
Microwave, uncovered, on HIGH for 3 minutes, whisking vigorously after each minute.
Remove from the oven and stir in half of the pear brandy.
Whisk again, then refrigerate, stirring from time to time.
To make the syrup, put the remaining sugar in a bowl with 1/3 cup (41/2 tablespoons) of water and heat in the microwave oven for 2 minutes on HIGH.
Mix until the sugar is completely dissolved, add the remaining pear brandy, stir and pour into a flat dish.
Peel and core the pear, set aside 1 or 2 slices for decoration and cut the rest into small cubes.
Fold carefully into the chocolate cream mixture.
Dip the ladyfingers (sponge fingers) one by one into the syrup, flat side only.
As you do so, line the base and sides of a 1 3/4 quart (1.75 litre/3 pint) charlotte mold (mould), curved side to the mold (mould).
Trim if taller than the sides of the mold (mould).
Pour half of the chocolate cream mixture into the mold (mould), cover with a layer of ladyfingers (sponge fingers) dipped in syrup, then the rest of the chocolate cream.
Finish with a layer of ladyfingers (sponge fingers), flat side upward.
Fill any little gaps with the trimmings.
Put a weighted board on top of the charlotte and refrigerate for at least 3 hours.
Melt in the microwave oven for 1 minute on HIGH.
Stir in the sour cream (creme fraiche) and beat thoroughly.
Invert the charlotte on to a plate.
Pour over the caramel syrup, then the melted chocolate and sour cream (creme fraiche) mixture.
Cut the slices of pear into decorative shapes and arrange on top of the charlotte.
Finish with rosettes of whipped cream.