Question: Why is a double boiler often used while making pudding?
About the article "Pudding", section "Creamy puddings".

Candidate passages:
The second and newer type of pudding consists of sugar, milk, and a thickening agent such as cornstarch, gelatin, eggs, rice or tapioca to create a sweet, creamy dessert.
These puddings are made either by simmering on top of the stove in a saucepan or double boiler or by baking in an oven, often in a bain-marie.
These puddings are easily scorched on the fire, which is why a double boiler is often used; microwave ovens are also now often used to avoid this problem and to reduce stirring.
Creamy puddings are typically served chilled, but a few, such as zabaglione and rice pudding, may be served warm.
Instant puddings do not require boiling and can therefore be prepared more quickly.
This pudding terminology is common in North America and some European countries such as the Netherlands, whilst in Britain egg-thickened puddings are considered custards and starch-thickened puddings called blancmange.
When wheat flour began to come into common use for making cakes and puddings, cooks in the north of England devised a means of making use of the fat that dropped into the dripping pan to cook a batter pudding while the meat roasted in the oven.
In 1737, a recipe for 'a dripping pudding' was published in "The Whole Duty of a Woman":Similar instructions were published in 1747 in "The Art of Cookery made Plain and Easy" by Hannah Glasse under the title of 'Yorkshire pudding'.
It was she who re-invented and renamed the original version, called Dripping Pudding, which had been cooked in England for centuries, although these puddings were much flatter than the puffy versions known today.
The Yorkshire pudding is meant to rise in a correctly executed preparation.
A 2008 ruling by the Royal Society of Chemistry has it that "A Yorkshire pudding isn't a Yorkshire pudding if it is less than four inches tall".
The Yorkshire pudding is a staple of the British Sunday lunch and in some cases is eaten as a separate course prior to the main meat dish.
This was the traditional method of eating the pudding and is still common in parts of Yorkshire today.
Because the rich gravy from the roast meat drippings was used up with the first course, the main meat and vegetable course was often served with a parsley or white sauce.
Traditionally, though less so now, the Yorkshire Pudding could be served as a sweet, with sugar, golden syrup, jam, or even with orange juice as a sauce.
It is often claimed that the purpose of the dish was to provide a cheap way to fill the diners, thus stretching a lesser amount of the more expensive ingredients as the Yorkshire pudding was traditionally served first. 
Persimmon pudding is a traditional American dessert made with persimmons.
Although American, persimmon pudding is similar to traditional English dessert puddings, such as Christmas pudding or quince pudding.
This style of pudding is generally either steamed or cooked in an oven with a water bath, or bain-marie.
These methods of cooking ensure the pudding remains moist and does not dry out or form a crust unlike the sweet but crusted persimmon bread.
The pudding is often served with ice cream, crème anglaise, whipped cream, apple sauce, or brandy butter.
It is best served warm, although it can be served cold as well.
Persimmon pudding lasts quite a while when refrigerated, and may be made in large batches to be served over the course of several days.
As the pudding ages the various individual flavors mellow and blend together.
In the U.S. state of Indiana, it is considered one of two legendary local dishes; the other being sugar cream pie. 
White pudding or oatmeal pudding is a meat dish popular in Ireland, Scotland, Northumberland, Nova Scotia, and Newfoundland.
White pudding is very similar to black pudding, but does not include blood.
Consequently, it consists of pork meat and fat, suet, bread, and oatmeal formed into the shape of a large sausage.
Earlier versions (pre-1990) often had sheep's brain added as a binding agent.
A similar pudding, known as Hog's pudding, is made in Somerset Cornwall and Devon though it is much spicier than white pudding, as it contains black pepper, cumin, basil, and garlic.
In Scotland, white pudding can also be known as mealy pudding and does not always take the form of a sausage.
It consists of suet, oatmeal, onions, and spices.
Some versions of Scottish white pudding are suitable for vegans, in that they contain no animal fat, vegetable fat being used instead.
The pudding may be cooked whole, or cut into slices and fried or grilled.
It is an important feature of the traditional Irish breakfast.
White pudding (as well as its black and red relatives) is also served battered at chip shops in Scotland as an alternative to fish (see fish and chips).
When served accompanied by chips, it is known as a white pudding supper. 
In the United Kingdom and most Commonwealth countries, "pudding" can be used to describe both sweet and savory dishes.
However, unless qualified, the term in everyday usage typically denotes a dessert; in the UK, "pudding" is used as synonym for a dessert course.
Dessert puddings are rich, fairly homogeneous starch- or dairy-based desserts such as rice pudding, steamed cake mixtures such as Treacle sponge pudding with or without the addition of ingredients such as dried fruits such as Christmas pudding.
Savory dishes include things such as Yorkshire pudding, black pudding, suet pudding and steak and kidney pudding.
In the United States and Canada, "pudding" characteristically denotes a sweet milk-based dessert similar in consistency to egg-based custards, instant custards or a mousse, often commercially set using gelatin or similar collagen agent such as the Jello brand line of products.
In Commonwealth countries these puddings are called custards (often shortened to curd) if they are egg-thickened, blancmange if starch-thickened, and jelly if gelatin based.
Pudding may also refer to other dishes such as bread and rice pudding, although typically these names derive from the origin as British dishes.