Caramelised Leek Tart Tatin

1) Pre-heat the oven to 160C (140C fan)
2) Lay some knobs of butter in the bottom of the baking tray, sprinkle with a pinch or two of sugar and plenty of fresh thyme and stand your leeks on top – they should all tuck together and stand up like little soldiers.
3) Drizzle with olive oil and place in the oven for at least an hour, so that it gently bakes and caramelises the leeks – check after 30 mins to ensure they’re not burning.
4) After an hour, take it out of the oven and drizzle a little balsamic over and around the leeks, then turn the oven up to 180C (160C fan) pop it back into the oven for another 15 minutes or until softened and lightly caramelised.
5) Take it out of the oven and set aside to cool a little, then once it's stop steaming, lay the sheet of pastry over the top, brush with egg wash and pop it back into the oven for another 20 minutes or until the pastry has risen and turned golden.
6) Remove from the oven and set aside for a few minutes to cool.
7) Take a knife and ensure that the edges of the pastry are loose from the pan, then place a plate or chopping board over the pan and quickly flip the whole thing upside down and remove the pan.