Heat the water, dates and pears in a medium-sized saucepan.
Bring to the boil then reduce the heat and simmer, until almost all the water has evaporated and the mixture is all soft. This takes about 25 minutes.
It should resemble a puree, but if it's still a bit chunky you can process until smooth in the food processor. Set aside until the cake bit is made.
Preheat oven to 180°C.
In a food processor or cake mixer, cream the butter and sugar together until light and fluffy. Reduce the speed and add the eggs.
Sometimes the mixture separates and starts to look like sour milk or something equally yucky. If this happens, add a spoonful of flour and give it a whiz. Things should return to normal.
Pour the mixture into a bowl, and fold in the flour and baking powder.
Add the date and pear puree, mix well and pour into the greased 24cm non stick cake tin with spring back sides. Bake for 45-50 minutes.
The sponge should be fairly firm in the centre and a knife should come out clean when inserted in the centre.
If not, cover with foil and cook for another 10 minutes. Set aside to cool while you make the toffee sauce.
Heat everything, except for the crème fraiche, in a medium sized saucepan. Bring to the boil, then reduce the heat and simmer for 10 minutes.
Remove from the heat, transfer to a bowl and allow to cool for about half an hour.
Whisk in the crème fraîche.
Unclip the side of the cake tin and, using a large knife, carefully slice the cake horizontally into two. This is a bit awkward but do your best, and if it falls apart, who cares! It'll all get drenched in toffee sauce so no-one will know.
Clip the side back on the cake tin and pour half the toffee sauce on to the bottom half of the cake.
Put the top half back on and pour over the remaining toffee sauce.
Cover with cling film (if sauce is leaking, put the whole lot into a roasting tin, or large plate) and keep overnight in the fridge, unless you are serving that day.
You can heat up the cake uncovered for about 15 minutes at 150°C before serving, or else serve it up cold. Whichever you prefer.