Preheat the oven to 200°C (180°C fan oven) Gas Mark 6 with a flat baking tray on the middle shelf. Put the bacon strips into a cold, non-stick, frying pan, then fry until golden. Stir in the spring onion whites for 1 minute, then tip into a bowl and leave to cool while you prep the tin.
Use the oil to lightly grease 8 holes of a large muffin tin (not a silicone one). Unroll the pastry and cut into 8 squares. Press a pastry square into each muffin hole to line, leaving the corners poking out over the top.
Add most of the parsley, the mustard, 2 eggs and some salt and pepper into the bacon mixture with the spring onion greens. Use a fork to beat everything together, then divide the mixture between the tarts.
Carefully crack a whole egg into each tart and sprinkle with the last of the parsley. Sit on the pre-heated baking sheet and bake for 25 minutes until the pastry is golden and egg firm. Lift the pies out with the help of a cutlery knife and enjoy warm or cold – with a dollop of red or brown sauce.