re:Dunno about the "suet ball of plum pudding" WW
Hard sauce! you can by it ready made, but its basicly confection (10X) sugar, butter (lots!) and a little cream..

but other desserts get soft custard, which in our house was just called "Birds" the brand name of the company that made the flavored powder mix.. in the north East, Birds is pretty much a staple good, and found in most stores.

Birds Custard is basically a cooked pudding (milk, sugar, vanilla flavor and some corn starch, heated till it thinkens.)but thinner.. it never gets as thick as pudding but always "pourable" like gravy. it can be "enriched" by adding an egg, and making it into a real custard.

In US, pudding is almost always a milk pudding, (sweetened, flavored milk, cooked with corn starch till thick, and cooled--but nowday, often instant-- no cooking needed)

Custard is similar, but it is thickened with eggs, (and is harder to make, since you need to heat the milk to thicken, but if you boil it, it tends to curdle. )

Both would be "soft solids" if molded into a cup, they could be unmolded and would keep there shape.(mostly, they would sag)