For the base:
Heat the milk and butter in a saucepan until hot but not boiling. Stir in the breadcrumbs, sugar and lemon zest, take off the heat and leave to steep for 10 minutes.Preheat the oven to 160˚C. Beat in the egg yolks and vanilla essence very thoroughly and pour this bread-thickened custard into a greased 1¼ litre oval or round dish. Bake at 160˚C for 20?30 minutes, until it?s firm on top, but still wobbly underneath. Leave to cool slightly.
For the filling:
Place all the filling ingredients in a saucepan and bring to a simmer. Simmer until you have a thick jammy sauce, stirring occasionally (there should still be plenty of whole blueberries).Remove from the heat and set aside.
For the topping:
Whisk the egg whites until stiff, then add half the sugar, one spoonful at a time, whisking continuously. Fold in the remaining sugar with a metal spoon.
To assemble the dish:
Pour and scrape the cooked blueberries onto the set custard base, spreading evenly. Dollop the meringue topping on top of the berries, making peaks with the back of the spoon. Sprinkle a little caster sugar over the top and place back in the oven for a further 20 minutes or until the meringue is golden and starting to crisp.