A chocolate is defined as any cocoa based sweet that does NOT contain nougat.
Chocolate in Borogravia
Nuggan, the state god of Borogravia, is very serious about setting prohibitions. Nuggan thinks that a god ought to prohibit things that people truly want, and so the prohibition has real effect on people's lives. So, Nuggan sets the prohibitions that his people shall eat neither chocolate nor garlic. This makes Borogravian citizens rather angry when finally they taste garlic and/or chocolate and find how tasty it is. For some time, devout and stern worshippers of Nuggan, the Nugganites, have been policing their villages to punish people who illegally possess chocolate. There is a profitable but dangerous black market for chocolate in Borogravia (see Monstrous Regiment). It is surprising, then, that Borogravia is mentioned (in Thief of Time) as a major source of fine chocolate, along with Quirm. Apparently the ban on consumption does not prohibit production for export. Perhaps this is to make the ban more noticeable?
Chocolate as weapon
In Thief of Time the Auditors of Reality incarnate as humans just for the sheer experience of it. They were bewildered by all the information received through the sensory organs on the human body. The sense of taste, especially, is powerful enough to render an incarnated Auditor unconscious. When very high-quality chocolate or other confectionery is used, an incarnated Auditor can "die". This happens because the human body of an incarnated Auditor is not grown in the usual fashion, but simply matter held together by the Auditor's careful design. The Auditor has to consciously hold the body together. When an incarnated Auditor tastes good chocolate, the surge of sensory input makes the Auditor lose control over the matter in the body, and the body dissolves into thin air. The same principle is used by the wizards in The Science of Discworld III: Darwin's Watch to remove non-incarnated Auditors from Roundworld. The chocolate in that case caused their "grey robe" manifestations to vanish.
Dwarf Chocolate carries a serious health warning. The Chocolate Museum in Vodorny Square in Bonk has selected examples and warns that this is not your normal sweetmeat. As with dwarf bread, it has been employed as a weapon of war. It also contains nuts. You have been warned.
Makers of chocolate
Wienrich and Boettcher of Zephire Street in Ankh-Morpork. This business does nothing so crass as to make chocolate. Herr Wienrich and Frau Boettcher create chocolate. There is a discreet drain just outside the window, lest people looking at the tastefully presented display drool too much. No prices are displayed. If you have to ask the price then you cannot afford the product - it's that sort of shop. Herr Wienrich and Frau Boettcher are evidently foreigners (Borogravian refugees from Nugganitic persecution?) and by inference are not members of the Guild of Confectioners. A regular customer, when she can afford one of their cheaper boxes, is Susan Sto Helit. The current Wienrich and Boettcher may, according to Susan, be descendants of the founders.
Lady Myria LeJean, a renegade Auditor in human form, identified "sugar, milk, butter, vanilla, cream, hazelnuts, almonds, walnuts, raisins, orange peel, various liqueurs, citrus pectin, strawberries, raspberries, essence of violets, cherries, pineapples, pistachios, oranges, lemons, coffee, cocoa..." before being cut short by an irritated Susan. Compare this to the ingredient list for Ankh-Morpork chocolate.
Higgs & Meakins are another Ankh business making better quality chocolate than normal. The true connoisseur will either avoid the nougat, however, or reassure themselves that a chocolate you don't like doesn't count, and dip back into the bag for another pick (and it had better not be dratted nougat again). After all, a chocolate you do not want to eat does not count as chocolate - this is a Well Known Fact. In the opinion of Susan, H&M do not in fact do good chocolate, but if a parent were to give her a box, she would never be so ill-mannered as to refuse it.