Preheat the oven to 160°C/gas 3.
Have the egg yolks ready in a bowl. Put the cream, milk, lemon zest and sugar into a pan and heat slowly until the sugar has dissolved, then pour over the egg yolks, stirring constantly. When all is mixed in, stir in the butter and breadcrumbs. Divide this custard between four ovenproof dishes and put these into a roasting pan.
Pour in enough boiling water around the dishes to come halfway up the outsides, and cook for 12–15 minutes, or until the custard is just set. Take out of the oven (but leave it on) and leave the dishes of custard to cool.
Put the rhubarb into an ovenproof dish with the orange zest, juice and sugar. Cover with foil and place in the oven for 30 minutes. Remove the rhubarb with a slotted spoon on to a plate, pour the juice into a pan and bubble up to reduce until very thick, then take off the heat and mix back the reserved rhubarb. Allow to cool.
When both the custard and the rhubarb are cool, put the egg whites into a heatproof bowl. Add the sugar and salt and place the bowl over a pan of simmering water, whisking until the temperature reaches 60°C on a sugar thermometer, then remove from the heat and whisk until cold, using an electric whisk. The mixture will double in size, form stiff peaks and be smooth and glossy.
Spread some of the rhubarb compote over the custard in the dishes, and spoon (or pipe) the meringue over the top.
Put into the oven for about 10 minutes, until the meringue is straw-coloured.