1 lemon, zest and juice
175g/6oz plum (or other) jam
25g/1oz caster sugar
100²µ/3Β½΄Η³ϊ caster sugar, plus extra for sprinkling
pinch fine sea salt
1 tsp vanilla extract
50g/1ΒΎoz unsalted butter, softened, plus more for greasing
4 large free-range egg whites (from eggs above)
4 large free-range egg yolks (whites reserved for meringue topping)
500ml/18fl oz full-fat milk
150²µ/5Β½΄Η³ϊ brioche, cut into slices and left to go stale (see recipe tip)