Preheat the oven to 200°C, 400°F, Gas Mark 6.

Place 125 g of the caster sugar and the butter into a 20 cm heavy based pan with an ovenproof handle over a low heat until the sugar dissolves.

Turn the heat up and cook until the caramel is nut brown, care needs to be taken so that the caramel does not get too brown and burn. (If it burns it cannot be used as it tastes too bitter).

Arrange the plums, standing up on their sides in a circular pattern, on top of the caramel.

Sprinkle 25 g caster sugar over the plums.

Cut the piece of ready rolled puff pastry in half and lay it over the plums tucking in the edges.

Bake in the oven for 20-25 minutes until the pastry is well risen.