The tonka bean is not the most visually appealing spice - the black, shrivelled seeds look rather like what a large rat would leave behind. My first encounter with it was not promising - a pastry chef mentioned that he had made some tonka bean ice cream. He showed me a bagful of the seeds and - being curious - I popped one in my mouth. The bitter intensity of the bean was almost overwhelming. I did some research and found that the tonka bean contains coumarin, a chemical that can cause liver damage if consumed in high doses (fortunately, one seed is not considered a high dose). For this reason, the bean is banned in the United States.
When used in desserts, its flavour becomes much more subtle and complex - it is often compared to that of the vanilla bean, but with spicy notes. Because they are very aromatic, tonka beans, which are harvested from trees in South America, are also used in perfumes and essential oil, in which they are said to work as an aphrodisiac and ease depression.
In cooking, grate the tonka bean on a fine-toothed rasp grater. It goes well with creamy, milky desserts such as ice cream (substitute tonka for vanilla bean) and custards. You can also mix the grated tonka bean into cookie dough or cake batter.
