Blancmange (pronounced “bla-monzh”) is a British dessert pudding made from milk thickened with a starch such as cornstarch (aka cornflour in the UK), or a gelatin such as agar (sea moss or isinglass.) The more thickener, the firmer the pudding. It is not thickened with rennet, the way Junket is.
Some people describe it as a form of custard. It is not really a custard, though, because custard is a term best reserved for something with eggs in it (though versions of Blancmange in the 1600s did have eggs.)
Blancmange is closer actually a stiffer version of those creamy desserts that North Americans call a pudding. It wiggles just like jellies. The texture makes some people gag, because it can be slithery.
It is usually sweetened with sugar, flavoured with vanilla and poured hot in a mould where it is allowed to set to have a nice shape, then turned out to serve. It can be garnished with berries, chopped fruits, or sweet sauces. It can also be made in individual serving dishes.
A popular commercial brand mix (if not the only one still extant), is “Pearce Duff”, made in South Yorkshire.
100g, prepared according to package directions (Pearce Duff brand, chocolate): 97 calories, 1.8 g fat, 17.1 g carbohydrates, 2.9 g protein
Pearce Duff brand instructions call for full-fat milk and 3 tablespoons (45g) of refined white sugar. You can reduce the calories and fat somewhat by instead using skim-milk, and a few drops of liquid Stevia. (We don’t know exactly by how much as we don’t have Nutrition FactsPer 100g, prepared according to package directions (Pearce Duff brand: Vanilla, Strawberry, Raspberry)AmountCalories100Fat3.6 gCarbohydrate14.4 gProtein2.9 g
The thickener in Blancmange has changed over the centuries.
Blancmange is believed to have originated with the Arabs. There are two different Arabic traditions: one uses rice, one uses almond milk. A rice, milk, and chicken breast tradition appears to have come out of Persia; an almond milk one out of Muslim-occupied Sicily and Spain.
Blancmange was being made in France in the 1200s, and was in England by the 1300s. Early European versions of Blancmange would use almond milk and or ground almonds, flavoured with rosewater. These early versions included shredded poultry, such as capon or chicken (sic). Veal could also be used if it was light — the idea was that all the ingredients in the dish should be “white.” The fat from the meat and the gelatin provided the set.
Many versions particularly in Italy were made with boiled chicken, almonds and rice.
Platina included a recipe for blancmange in his mid 1400s cookbook. He called for almond milk, ground deboned chicken, bread sauce, ginger and sugar. The mixture was to be strained, simmered, then flavoured with rosewater. After setting, it was sprinkled with pomegranate seeds as a garnish.
Blancmange was considered invalid food, as well as food good enough for a feast, as it was a lot of work to make.
By the 1500s, meatless versions were being made, and cream and eggs were being used instead of almond milk. In the 1600s, it was thickened with jelly made from calves foot or ground deer antlers. In the 1800s, arrowroot was used as a thickening starch.
Fannie Farmer, in Boston Cooking School Cookbook (1896), gave two recipes for Blancmange, both thickened with Irish Moss.
The Pearce Duff brand has been made since 1847. It comes in three flavours. And, as of 2006, sales are increasing by 7 percent a year.
Another major brand historically was Brown and Polson, which had one-third of the market up until the end of the 1980s, but the company ceased production of its blancmange sometime after that. 
Literature & Lore
Wilt du machen einen blamensier
Wie man sol machen einen blamenser. Man sol nemen zigenin milich und mache mandels ein halp phunt. Einen virdunc ryses sol man stozzen zu mele. und tu daz in die milich kalt. und nim eines hunes brust, die sol man zeisen. und sol die hacken dor in. und ein rein smaltz sol man dor in tun. und sol ez dor inne sieden und gibs im genue. und nimme ez denne wider und nim gestozzen violn, und wirfe den dor in. und einen vierdunc zuckers tu man dor in und gebs hin. Also mac man auch in der vasten machen einen blamenser von einem hechede. If you want to make a blancmange
This is how you should make a blancmange. One should take goat milk and make a half phunt almonds. Pound a quarter phunt rice to meal. And put that into the cold milk. And take a hen’s breast, which one should tease. And chop it into the mixture. And add a clean fat therein. And one should boil it and give it enough (time) and then take it again (off the heat) and take beaten violet, and throw it therein. And a quarter phunt sugar. Add that in and give out. Also, in the fast (days), one may make a blancmange from a pike.
— Ein Buch von guter spise. Recipe 3. Translation by Alia Atlas. Retrieved April 2009 from http://cs-people.bu.edu/akatlas/Buch/buch.html.
Original manuscript hails from Würzburg between 1345 and 1354.
Blancmange was the name of a music group form by Neil Arthur and Stephen Luscombe from 1980 to 1986.
Monty Python (Flying Circus, Episode 7) had a skit in which an Angus Podgorny played tennis at Wimbledon with a blancmange as his opponent. Podgorny won because spectators rushed onto the court and ate his opponent.
Blancmange is mentioned in Geoffrey Chaucer’s (1340 or 1344 to 1400 ) Canterbury Tales:
A COOK they hadde with them for the nones [Ed: occasion],
To boil the chickens and the marrow bones,
And powder merchant tart and galingale.
Well could he know a draught of London ale.
He could roast, and stew, and broil, and fry,
Make mortrewes, and well bake a pie.
But great harm was it, as it thoughte me,
That, on his shin a mormal* [Ed: open running ulcer] hadde he.
For blanc manger, that made he with the best .
Cooks would often prepare food sitting with the cauldron or crock between their legs. Chaucer is definitely seeking to cause revulsion in his readers out here, by causing them to picture an open sore running into a pot of blancmange.
Blancmange means “white eat” in French; “blanc” meaning “white” and “manger” meaning “eat.” It is pronounced “bla-monzh” in English.
For the Blancmange (“manjar blanco”) made in Chile and in Panamá, see the entry on Dulche de Leche.
Margolis, Jonathan. Old food brands that refuse to die out. The Independent. London. 14 March 2006.
 “Another major puddings market is blancmange, where Brown & Polson (CPC) accounts for one-third of market sales. The same company also dominates a very similar product with a different use: cornflour. Other companies with interests in both products, albeit on a smaller scale, include Pearce Duff (Dalgety), Hazelwood Foods, and Rowntree Mackintosh (Nestlé).” — Mark, John, and Robert Strange. Food Industries: Reviews of United Kingdom Statistical Sources. Volume XXVIII. London: Chapman & Hall. 1993. Page 508. [Ed: “…review is believed to represent the position, broadly speaking, as it obtained in mid-1989, but a few minor revisions have been made to update the main text during the proof-reading stage in mid-1991.”]