1. Preheat the oven to 200°C/gas mark 6. Divide the pastry into 4 rectangles, about 15 x 10 cm and transfer to a baking sheet. Score a border about 1 cm from the edge, making sure not to cut all the way through. Prick the middle of each rectangle with a fork. Beat 1 egg with the milk and use to brush the border. Bake in the oven until puffed up and golden, about 10 mins.
2. Meanwhile, blanch the spinach in boiling water until just wilted, no more than a minute or so. Drain and dry thoroughly, using a dishcloth to squeeze out any excess liquid then roughly chop. Flatten the centre of the pastry bases slightly, then spread with the hollandaise. Scatter the salmon and spinach evenly between the cases and crack an egg into each one. Don’t worry too much if the whites spill over a little.
3. Bake until the eggs are set, about 10-12 mins. Scatter over with the dill and red onion and serve with the rocket and tomato salad.