Butter or spray with non stick spray a 9in/ 23cm tart tin with a removable base. Preheat oven to 350°F/180°C
Beat butter and sugar together until combined. Add egg yolk and beat in thoroughly. Stir in flour until it form a soft dough. Don't over mix.
Roll out the dough between two sheets of non stick baking paper that has been floured. While rolling check that the dough isn't sticking. If so, sprinkle with extra flour.
The dough should be a about ¼inch or 6mm thickness. You will have a bit of pastry leftover - check in the "recipe notes" for tips on what to do with the extra pastry.
Use the pastry to line the tart tin.
If you have time chill for 30 minutes.
Make the filling
Beat butter and sugars until pale and fluffy.
Add in eggs, ground hazelnuts and flour. Beat to combine.
Stir in melted chocolate.
Spoon into pastry case and smooth out the top.
Prepare the pears.
Peel pears. Cut in half length ways and scoop out the core. Turn the halves onto their cut side and use a sharp knife to cut parallel the long way down the pear leaving a small amount attached at the tip. Make the slices quite thin that way they will cook through. Repeat with remaining pear halves.
Fan out the pears and arrange on the tart. Press down lightly.
Bake the tart for 45 minutes or until firm and the pastry is golden brown.
Leave to cool. Dust with icing sugar to serve.
There will be about a quarter of the pastry left. It is delicious so don't waste it. Roll it into small balls. Press an indentation in the middle, fill with jam and bake at 180C (350F) for 12-15 minutes or until golden. If you don't like jam, top the balls with a large chocolate drop or dip into sugar/nuts before baking.
No Frangelico? Rum or marsala are good. Otherwise leave it out.
If you have time,toasting the ground hazelnuts will bring out the flavour
This tart can be prepared up to being filled and then refrigerated overnight. Peel and prepare the pears just before baking.