Separate three of the eggs into two bowls. Add the fourth egg to the egg yolks and beat until well combined. Stir in the milk, followed by the breadcrumbs. Cover the egg whites with clingfilm and set aside until needed.
Spread the raspberry jam on the base of a pie dish. Pour over the milk mixture and then set aside for 30 minutes to allow the breadcrumbs to swell up.
Preheat the oven to 150C (300F/Gas 2). Place the pie dish in the oven and bake for 1 hour until the custard is set and firm to the touch.
Using an electric beater, whisk the egg whites until stiff, then fold in the sugar to make a smooth meringue. Swirl the meringue on top of the set breadcrumb mixture and return to the oven for 15-20 minutes or until the meringue is set and golden. Serve warm straight on to the table with a separate jug of custard to hand around.