Before the development of the modern enclosed stove in the 19th century, cooking techniques were very different to what we consider "normal" now. Meat was roasted on a spit in front of the fire (meat cooking in an oven is actually "baked", not roasted), or boiled in a large pot over the fire, food was grilled or broiled using a gridirons, pots had legs to keep them stable on their bed of charcoal, coal or peat. Puddings, sweet and savoury, were originally cooked in animal guts, as they make good, cheap, readily availble vessels. Depending on what species or part of the animal used, these guts either gave you long sausages of various lengths (using the intestines) or a round pudding (if using the stomach for instance). These puddings could be fried of grilled (just like a modern sausage) or boiled in a pot. The haggis is the last British version of one of these early boil-in-the-stomach puddings.
Sometime during the 16-17th century the stomach was replaced to a large extent with a cloth. It has been suggested that this was to avoid the fllavors associated with the gut, but it is equally likely that people with less ready access to guts were now making puddings and neaded a replacement. While British historic and regional cookery is busting at the seams like an over stuffed sausage with pudding recipes, even until quite recently the women of Sussex were famous for their making pudding skills.In the 1930's it was still common for puddings in this region to be boiled in a cloth, rather then being made in a basin.
"Sussex Pond Pudding" is still popular with people that like to make traditional English recipes, the modern versions is now made in a bowl and contains a whole lemon with a butter/sugar sauce. The "Pond" is said to be the butter sugar sauce that runs out of the pudding when cut. This is a 17th century version, the oldest I have found, you can see that the pond was originally something quite different.
From “The Queen Like Closet” by Hannah Woolley, 1672.
"To make a Sussex Pudding"
"Take a little cold cream, butter and flower, with some beaten spice, eggs, and a little salt. Make them into a stiff paste, then make them into a round ball, and you mold it, put in a piece of butter in the middle; and so tye it hard up in a buttered cloth, and put it into boiling water, and let it boil apace till it be enough then serve it in, and garnish your dish with barberries; when it is at the table cut it open at the top, and there will be as it were a pound ["pond"] of butter, then put rosewater and sugar into it and so eat it.
In some of this like paste you may wrap great apples, being pared whole, in one piece of thin paste, and so close it round the apple, and through them into boiling water, and let them boil till enough, you may also put some green gooseberries into some, and when wither of these are boiled, cut them open and put in rosewater butter and sugar."
Almost one hundred years later William Ellis describes making of a near identical pudding in ""The Country Housewife's Family Companion", 1750".
"There are two ways of making this famous pudding.........The other way is, to make a round pudding of the same ingredients [flour, butter, milk and eggs], which (I suppose) is to be tied up in a cloth, and the middle of this pudding they put a piece of butter, and so inclose it in the dough that the butter cannot boil out . When boiled enough, they find the butter run to oil, and well soaked into the pudding, that the eat it with meat instead of bread, or without meat as a delicious pudding."
As it shares a border with Sussex, it comes as no surprise that Kent also has a similar pudding, known as a "Kentish Well Pudding". This recipe is from Eliza Acton's "Modern Cookery for Private Families", 1845.
A Kentish Well Pudding
"Make into a smooth paste, with cold water, one pound of flour, six ounces of finely-minced beef-suet, three quarters of a pound of currants, and a small pinch of salt, thoroughly mixed together. Form into a ball six ounces of good butter, and enclose it securely in about a third of the paste (rolled to half an inch thickness), in the same way that apple-dumpling is made; roll out the remainder of the paste, and place the poprtion containing the butter in the centre of it, with the part where the edge was drawn together turned downwards: gather the outer crust round it, and having well moistened the edge, close it with great care. Tie the pudding tightly in a well-floured cloth, and boil it for two hours and a half. It must be dished with caution that it may not break, and a small bit must be cut directly from the top, as in a meat pudding."
As you can see Acton's recipe is almost identical in outcome to that of Woolley's. As discussed by Mary Norwark in her excellent "English Puddings", today the Sussex and Kentish puddings are distinguished by the addition of either a whole lemon or dried fruit to the butter centre, respectively.