1. Process the stale brioche into crumbs and tip into a mixing bowl.
2. Grease your pie dish, (6-cup oval dish, 11x8x2) with butter and preheat the oven to 325˚
3. Warm the milk in a saucepan along with the butter, lemon zest, vanilla, sugar, and a pinch of salt just until the butter’s melted.
4. Whisk the yolks in a large bowl or pitcher, pour the warm milk mixture on top, and whisk to combine, then pour this over the crumbs in their bowl and leave for 10 minutes, before transferring to the greased dish. Bake for 20 minutes, or until the top is just set, although the crumb-custard will still be wibbly underneath.
5. Take the dish out of the oven; the custardy brioche will firm up a little on the surface while it stands, waiting.
6. IN a small bowl, whisk the lemon juice with the preserves, you want a soft, pourable consistency. If the preserves are too thick, simply warm in a small saucepan. Set aside while you get on with the topping.
7. WHisk the egg whites in a grease free bowl until they form firm peaks, then gradually whisk in the superfine sugar, until you have a thick and shiny meringue.
8. Pour the lemon-spritzed preserves over the crumb-custard, smoothing it, with the lightest touch, over the top. Cover the preserves-topped custard with the meringue, making sure it comes right to the edges to seal it well. Use a fork to pull the gleaming meringue topping into little peaks, and sprinkle with ½ teaspoon or so of superfine sugar.
9. Put the dish back in the oven and bake for about 20 minutes until the meringue is bronzed and crisp on top. Let it stand out of the oven for about 15 minutes before serving.