The one vulnerable aspect of chocolate is its extreme dryness, and the vast number of tiny sugar and cacao particles whose surfaces attract moisture. If a small amount of water is stirred into molten chocolate, the chocolate will seize up into stiff paste. It seems perverse that adding liquid to a liquid produces a solid: but the small amount of water acts as a kind of glue, wetting the many millions of sugar and cocoa particles just enough to make patches of syrup that stick the particles together and separate them from the liquid cocoa butter. It’s important, then, either to keep chocolate completely dry, or to add enough liquid to dissolve the sugar into a syrup, not just wet it. It’s therefore best to add solid chocolate to hot liquid ingredients, or pour the hot liquid all at once onto the chocolate, rather than add the liquid gradually to molten chocolate. Seized chocolate can be salvaged by adding more warm liquid until the paste turns into a thick fluid.