Kasundi Tatka is a popular Bengali condiment, a tangy and spicy mustard sauce often served as a side with various dishes. It's made using mustard seeds, green chilies, and sometimes raw mango or other souring agents. The fresh, zesty flavor makes it a perfect accompaniment to fried fish, snacks, or rice dishes. The term "tatka" refers to the fresh or raw style, emphasizing the intense, sharp taste of mustard.