Preheat the oven to 220°C/200°C Fan/Gas Mark 7. Unroll the puff pastry sheet and place on its paper onto a baking tray. Using a sharp, small knife cut a 1.5cm border around the edges (making sure not to cut all the way through). Prick the inside of the pastry all over with a fork.
Place in the oven and bake for 20 minutes, until golden and puffed. Remove from the oven and, using a spoon, carefully push the inside of the pastry back down. Cool for 10 minutes.
Meanwhile, bring a medium pan of water to the boil and add the eggs. Boil for 7 minutes then lift out and run under cold water to cool. Peel and cut into quarters.
Add the asparagus to the boiling water along with a generous pinch of salt and cook for 5-7 minutes until soft, but still with a little bite. Drain under cold water to cool and set aside.
Spread the inside of the pastry with the cream cheese. Top with the asparagus spears, smoked salmon and quartered eggs. Season lightly with salt and pepper and sprinkle over the chives. Cut into 15 squares to serve.