Roll the pastry out into a circle large enough to cover a small ovenproof frying pan or tatin dish of about 20cm/8in in diameter. Place the pastry in the fridge to rest until needed.
Preheat the oven to 200C/400F/Gas 6. Peel the onions and slice into thick rounds. Remove the outer sections of the fennel and cut each bulb into six pieces, removing some of the woody core.
Take the stalk off the chilli but leave it whole. Cut a slit down the length so the juices can escape and flavour the vegetables.
Put all the vegetables into a roasting tin, with the onions laid flat on the bottom of the tin. Pour over the olive oil and balsamic vinegar and add the crushed coriander seeds, salt and pepper.
Roast in the hot oven for 15-20 minutes, turning occasionally but being careful to keep the onion rings in one piece.
Directly in the frying pan or tatin dish, mix the sugar with three tablespoons of water. Quickly bring to the boil and cook, without stirring, until golden-brown.
Arrange all the vegetables in a decorative pattern in the frying pan or tin and press down tight. Sprinkle with the thyme and parmesan.
Cover with the puff pastry and tuck in at the edges between the vegetables and the sides of the pan. Prick the pastry with a fork and bake for 25-30 minutes, or until the puff pastry is golden-brown and fully cooked. Leave to cool for at least five minutes before turning upside down onto a serving dish.
Slice and serve with a side salad.
Turn it over and voila. Caramelised lushness!
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