Preheat the oven to 180 C / Gas 4. Line a tart tin with the shortcrust pastry.
For the filling, combine the syrup, lemon juice and breadcrumbs in a mixing bowl and then spoon into the pastry case.
Crush the cornflakes lightly with your hands and sprinkle them over the top of the tart. Bake in the preheated oven until golden brown, about 20 minutes. Serve with vanilla ice cream.