Cut the pastry into 6 pieces, then roll each piece out on a lightly floured surface and trim to a 15 cm (6 inch) circle using a saucer as a guide. Transfer to 2 large, lightly oiled baking sheets. Mark smaller circles 2.5 cm (1 inch) in from the edges, then prick all over the inner circles with a fork.
Bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 10 minutes until well risen. Press down the centre with a fork and cook for a further 5 minutes until the tart cases are crisp and golden.
When the tart cases are almost ready, heat the butter in a frying pan, then add the spring onions and fry until softened. Add the peas and cook for a few minutes until hot, add the lettuce and cook for 30 seconds, then stir in the mint, crème fraîche and salt and pepper.
Spoon the pea mixture into the hot tart cases and arrange the smoked salmon in folds on top. Sprinkle with a little extra pepper and serve at once with salad.