In its thin puff pastry case, this lemon pudding would have resembled tarte au citron, only the lemon custard is stiffened with breadcrumbs (the pith of a ha’penny loaf).
Until the 19th century, bread prices were regulated by an assize: an official scale that linked the cost of bread to the price of wheat. The weight of a halfpenny loaf therefore fluctuated over the course of the 18th century.
In 1758, the Lord Mayor of London ruled that a white halfpenny loaf weighed 3 oz 1 drachm. Wheaten bread at the same price weighed 4 oz 10 drachms. Later in the century, poor harvests and the inflation and shortages caused by the French Revolutionary Wars resulted in higher bread prices for Londoners.
A lemon pudding
Pare the outward rind of 4 lemons & squeese out all the juice clear. Take the pith of an hapenny loaf, crumble it in half a pint of whit[e] wine, bruse it very well & mix it with your juice & rine, 6 or 8 eggs, half the whites, half a pd of melted butter, half a pd or more of powder sugar. Paste yr dish very thin. A little time bakes it. Take care it dos not scortch.