Brush the pastry with some of the beaten egg, then sprinkle with the muscovado sugar and orange rind. Roll one edge of the pastry until it reaches the centre. Do the same from the opposite edge until both rolls meet.
Brush the pastry with more beaten egg, then cut into 8 thick slices. Lightly oil a baking sheet with spray oil. Arrange the pastry slices, cut side-up, on the prepared baking sheet. Bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 10 minutes until well risen and golden.
Meanwhile, put the orange juice and caster sugar in a saucepan. Add the plums and cook, stirring, over a medium heat for 5 minutes.
Sandwich the palmiers together in pairs with the plums, dust with icing sugar and serve with a spoonful of crème fraîche.