Kasundi

Kasundi is the Bengali variety of mustard sauce or relish. It has the pungent paste of fermented mustard seeds, spices and sometimes dried mangoes, dried Indian plum and olives. Kasundi is popular as a dipping sauce in Bengali cuisine. Kasundi is a mustard sauce made by fermenting mustard seeds, and is much stronger and sharper than other kinds of mustard sauce. It is highly pungent, and is capable of exciting the nasal passage and bringing tears to the eyes in the same way as wasabi. The descriptions by famous chefs outside Bengal as the “answer to the ketchup”, “ketchup with a lot more going on”, or “a rich, unctuous tomato sauce of Indian origin” are based, according to food writer Pritha Sen, on mistaken notions. In modern times, Kasundi is popularly served with Bangladeshi snacks like cutlets and chops, and deep-fried spicy treats, as it brings tartness and pungency to the flavours. It also can be served as a dip with other snacks, as well as sandwiches, pizzas, burgers, omelettes, salads and other food. But, traditionally it was served neither with these treats nor in such quantities at home. In the past, it was stored with care, served sparingly and in small quantities, and paired with hot stir-fried greens, never fish or meat. The practice of pairing kasundi with non-vegetarian dishes evolved in the commercial eateries, beginning with batter-fried fish.

Source: Wikipedia