Preheat the oven to 200c/ 180 fan assisted ovens/gas mark 4. Line a baking tray with greaseproof paper.
Open the Pain au raisin cans. Using a sharp knife slice each roll of dough into 6 equal slices.
Take the strip of pastry on the top left and bring it across the blueberries, repeat with the strip of pastry on the top right. Repeat, working down until you have a plaited pattern and all the lengths of pastry have been crossed.
Gently press the top and bottom ends to seal and brush with the top and sides with beaten egg. Bake for 10-12 minutes. Cover with foil and continue to cook for a further 8-10 minutes, until the pastry is golden and cooked through. Remove onto a wire rack and let cool.
Add 1 tsp of water to the pot of icing sugar, then mix in a few drops of water at a time until you have a thick drizzling consistency. Drizzle over the plait, then decorate with the reserved blueberries. Serve with natural yoghurt, if liked.