This stock is used in the same way you would use a dark chicken stock or other meat stock. It works well as a base for sauces and soups, and if you are feeling under the weather it is nice for when you don’t want to actually eat, but want some nutrition. It is really nice heated up with some fresh ginger in it. In meat stocks, the agent that thickens it is gelatin. In vegetables, the equivalent is pectin. By charring the onions and sautéing the rest of the vegetables, the pectin is catalyzed and so more readily available to the stock. Konbu* is a type of kelp. Seaweeds are used commercially as a thickener in many things, from toothpaste to ice cream, and is used that way here.