From Discworld & Terry Pratchett Wiki

Rock-hard (and indeed contains various rocks such as gravel), never goes stale, and is terribly sustaining. A traveller can go for miles, just knowing there's dwarf bread in their pack. A traveller can think of just about anything to eat rather than dwarf bread including their own foot and even pumpkins (see Witches Abroad).

Various forms of dwarf bread can be used as weapons, e.g. battle muffins and drop scones. Fine specimens of dwarf bread can be found in the Dwarf Bread Museum, Whirligig Alley, Ankh-Morpork, open to the public whenever volunteers have time (Feet of Clay). Dwarfs away from home often miss dwarf bread very much, and complain that mass-produced breads by Mr. Ironcrust hardly meet the standards, but dwarfs are too busy working to go and see the exhibits in the museum, much less to volunteer there.

Proper dwarf bread has to be not just baked, but forged (with gravel, of course) and dropped in rivers and dried out, and sat on and left, and looked at every day and then put away again. For preference, its use as a cat's litter box is also recommended. Dwarfs generally devour it with their eyes, because even dwarfs have trouble with devouring it any other way.

Famous breads include the Scone of Stone, which appears in The Fifth Elephant.

Other instances of dwarf bread include:

that made by Carrot's mother which he can barely get out of the box by himself, and has to cut with his pike.

the Battle Bread of B'hrian Bloodaxe.

the bread offered to the dwarfs outside Genua which was all the better for Greebo pissing on it.

the bread that Nanny Ogg promises to bake for Casanunda for which an unemptied cat litter tray and gravel will form essential components.

The Compleat Discworld Atlas notes, for the first time, the existence of Dwarf Chocolate which comes from the same sort of kitchen and uses the same catering philosophy.

Annotations

Hard tack anyone?

Also, cram anyone?

On the theme of the Dwarf Bread Museum, there is a museum in Paris, commemorating the privations of the city's prolonged siege by the Prussians in 1870, which preserves, as good as new after 141 years, samples of the sorts of bread that were being baked in Paris at the height of the siege. Some of these might have been hopelessly contaminated by having flour in them, but wood shavings, sawdust and the occasional bit of gravel, brick-dust and pulverised stone feature heavily. These examples of extreme bakery are kept under glass in controlled conditions, but are as good as the day they were first forged.

The Musée de la ville de Paris at the Musée Carnavalet also houses proof of the cuisine du rat that grew up during the siege, a cooking style known as 'siege game", and which was turned into a great new culinary experience. The French took pride in their creativity and ingenuity and a rat cooked by a French chef must have felt jolly grateful for it.

From tvtropes: Ship's biscuits or hardtack, a very durable cracker/biscuit, has a few samples in museums that are a century and a half old. Some say the "hardtack made 140 years ago 'tastes just as good' now as it did back then." This is not an impressive claim; however, it may be as close to dwarf bread as reality will allow. There was one incident which some people made some hardtack according to the old recipes and fired it from a cannon. It went over a hill and through the windshield of a parked car. The hardtack was undamaged (The people performing the experiment paid to replace the windshield).

1970's British comedy trio The Goodies did the classic "Ecky Thump!" episode which was a spoof on martial arts movies. In an overview of little-known schools of fighting round the world, they introduced a French martial art called Oh-Hon-Hee-Hon, involving hitting people with long stale baguettes. See it here at 6:53 onwards. (although the whole thing is pretty damn funny).