Mustard seeds are one of the oldest spices used in European and Indian cuisine. These little round seeds come in three varieties (yellow, black and brown) from three different plants that belong to the cabbage family. Mustard seeds are crushed to make the various mustards you find from around the world. In Indian cooking, particularly in the South, the small black variety (actually a dark reddish-brown) is extensively used - the whole seeds are fried in hot oil for about 10-15 seconds until they crackle and pop. This releases a deliciously toasty or nutty flavour into the oil that goes particularly well with dhals, vegetarian dishes and most curries.