Reserve one-third of the pastry for the lattice. Roll out the remainder on a lightly floured surface until large enough to line the base and sides of a buttered metal pie dish, 20 cm (8 inches) in diameter and 5 cm (2 inches) deep. Lift the pastry over a rolling pin, drape into the dish, then press over the base and sides.
Mix the sugar, cornflour and lemon rind together, then add the fruits and toss together gently. Pile into the pie dish. Trim off the excess pastry, add to the reserved portion, then roll out. Cut into 1.5 cm (¾ inch) wide strips long enough to go over the top of the pie.
Brush the top edge of the pie with milk and arrange the pastry strips over the top as a lattice. Trim off the excess. Brush with milk, then sprinkle with a little sugar.
Bake in a preheated oven, 190°C (375°F), Gas Mark 5, for 30–35 minutes until golden. Leave to cool for 15 minutes, then serve cut into wedges, drizzled with melba sauce.