Carrageen Mould is an Irish milk pudding thickened with seaweed. It ends up something like a blancmange.
It is made from milk, dried Carrageen (aka the seaweed known as Irish Moss), and sugar. Some versions add egg; some add flavouring such as lemon rind or rum.
To make, you wash the seaweed well, then rehydrate it by soaking it in water for 10 minutes. Meanwhile, be warming the milk and sugar (and any flavouring) for 10 minutes, stirring occasionally.
Then, drain the seaweed, add it to the warmed milk, and bring to a simmer for 20 minutes, stirring occassionally. Strain the moss out and discard, put the milk into a mould, and let stand at room temperature until set. Turn out to serve, usually with cream and / or fruit.
Literature & Lore
There were also more elaborate versions, such as that recommended by Eliza Leslie:
“Carrageen Blanc-Mange
This is made of a sea-weed resembling moss, that is found in large quantities on some parts of our coast, and is to be purchased in the cities at most of the druggists. Carrageen costs but little, and is considered extremely salutary for persons of delicate constitutions. Its glutinous nature when boiled, renders it very suitable for blanc-mange.
From a quart of rich unskimmed milk take half a pint. Make the half pint of milk as sweet as possible with powdered white sugar, and put into it the grated peel and the juice of a large lemon, and a large stick of cinnamon broken up; also eight or nine blades of mace. Set it in a close pan over hot coals, and boil it till all the flavour is extracted from the lemon and spice. In the mean time wash through two or three waters half a handful of carrageen, (if you put in too much it will communicate an unpleasant taste to the blanc-mange,) and add it to the pint and a half of cold milk. Then when it is sufficiently flavoured, stir in the boiled milk, adding gradually half a pound of powdered sugar, and mix the whole very well. Set it over the fire, and keep it boiling hard five minutes from the time it has come to a boil. Then strain it into a pitcher; wet your moulds or cups with cold water, put the blanc-mange into them, and leave it undisturbed till it cono-eals.
You may substitute for the lemon-peel and juice, ten drops of essence of lemon, stirred into the milk after you have put to it the carrageen, etc. Or you may use instead, a few drops of extract of roses, or a wine glass of rose water.”
— Leslie, Eliza. Carrageen Blanc-Mange. In: Directions for Cookery. 1837.
Sources
Boyd, Lizzie, ed. British Cookery. 2nd Edn., Christopher Helm, 1977, Page 417.
Ellis, Leslie. Seaweed recipes: Carrageen chocolate jelly. London: Daily Telegraph. 4 June 2009.