For the oil sardines in a sleeping skirt, first defrost puff pastry, roll out thinly on floured work surface. Cut into 8 squares with edges slightly longer than an oil sardine.
Drain the oil sardines and divide among the pastry pieces. Spread about 1 tsp of tomato ketchup on each of the sardines. Close the dough around it to form a roll. Brush the long seam and sides with a little egg white and press together. Place seam side down on a baking sheet rinsed with cold water, brush with egg yolk and bake in a preheated oven at 250 °C until golden brown. Serve the oil sardines in their sleeping skirts while still warm.
Preparation Tip:
Serve the oil sardines in their sleeping skirts on fresh leaf salads.