Use a 23cm ( 9-10in) tart case with a removable bottom. Set the oven to 180C or 350F
Make the pastry by adding the flour and sugar to a food processor along with chilled cubed butter and a small pinch of salt and blitz this mixture till it is combined and looks a bit like dried crumbs. Mix the egg and chilled water and beat together. Add all but a tiny drop of the egg mix and blitz. The pastry should come together in a soft ball. If there are still a lot of dry bits then add the rest of the liquid and blitz again.
Turn onto a bench and flatten the dough, wrap in plastic and put into the fridge till chilled.(20 minutes)
Once rested bring the dough out and let it soften 5 minutes before rolling to fit your tart case. You can roll it out with a little flour and put it between a couple of pieces of baking paper. Put the prepared tart tin in the fridge to firm up the pastry (15-30 minutes), the freezer works well.
Bake the pastry case blind ( Line with paper, fill with beans and bake. Remove the paper after 15 minutes and finish baking the tart without the beans and paper till golden, Cool)
Using an electric mixer beat the butter and icing sugar till very light in colour and fluffy. Add the eggs one at a time and them the cocoa. beating all the time. Add the flour of nut meal and beat through. Set this aside (It can be done the day before, take it out of the fridge and let it come to room temperature before using)
Put cut bananas onto the tart case and then spread the frangipane on top.
Bake for 30- 35 minutes testing by pressing your finger tips into the middle. It will be soft but have a little give. Cool
Have all of the ingredients ready including the butter cut into cubes, the cream and a whisk.
Put the sugar into a small saucepan. Swirl to combine the liquid and dissolve the sugar. When the sugar is dissolved turn the heat up a little. Watch while it starts to colour. I like to let it get very dark before adding the cream and stirring. Take off the heat. Next add the butter 1/3 at a time whisking well. You will end up with a dark shiny sauce. Add a 1/4 teaspoon of flaked or sea salt and stir. Pour onto the tart and tilt from side to side so the caramel spreads easily
You can replace hazelnut: 200 gm almond meal
Use unsalted butter to reduce over salting in caramel