Scrub the potato under running water.
Pat dry on kitchen paper.
Prick in several places with a fork.
Put in the center of the microwave oven on kitchen paper and microwave for 6 minutes on HIGH.
Cover the potato with a cloth and leave to stand for 5 minutes.
Break the chocolate and melt in a bowl with the butter for 1 minute on HIGH.
Stir well.
Whisk the eggs in a bowl.
Peel the potato and mash with a fork.
Add to the melted chocolate and butter mixture along with the beaten eggs, sugar, sour cream (creme fraiche), coffee extract (essence) and caramel syrup.
Beat thoroughly.
Sift the yeast over the mixture and stir again.
Oil the base of a 9 inch (23 cm) souffle mold (mould) and line with a circle of oiled non stick parchment (greaseproof paper).
Spoon the mixture into the mold (mould) and micro wave for 10 minutes on HIGH.
Leave the cake to cool in the container.
Turn out on to a platter and remove the non stick parchment (greaseproof paper).
Surround with the pear halves in syrup.
Cut the can died orange zest (peel) into 4-6 diamonds and put one on each pear half.
Add the pear liqueur to the custard and pour into a jug.