Preheat the oven to 180°C (350°F).

Peel and core the apples.

Cut the peeled apples in half lengthwise.

Combine 330 g caster sugar and 1 litre water in a saucepan.

Bring the syrup to a gentle simmer, stirring until the sugar dissolves.

Add the apple halves to the simmering syrup.

Poach the apples slowly for about 20 minutes until tender but still holding their shape.

Lift the poached apple halves from the syrup and set them aside to cool slightly.

Combine 600 g caster sugar and 200 ml water in an ovenproof pan.

Cook the sugar mixture until it becomes a deep golden, loose caramel, about 15 minutes.

Remove the pan from the heat while the caramel is still soft and spoonable.

Spoon enough caramel across the base of the ovenproof pan to coat it completely.

Arrange the apple halves tightly over the caramel with their cut sides facing up.

Press the apple halves gently into the caramel.

Roll the puff pastry into a 4 mm thick disc wide enough to cover the pan.

Lay the puff pastry disc over the apples and tuck the edges into the pan.

Bake for 20 minutes until the caramel is bubbling, glossy, and deeply flavored.

Rest the tart for 5 minutes, then carefully invert it onto a serving plate while still warm.