Tewkesbury mustard is a blend of mustard flour and grated horseradish root. the mustard was developed in the english town of tewkesbury in gloucestershire, and gained a certain reputation in the 17th century, becoming a staple condiment of the kitchens of the time. shakespeare mentions the mustard in henry iv, part 2, in which falstaff has the line: “his wit's as thick as tewkesbury mustard” (act 2, scene 4, line 244), describing the character of his friend ned poins.

Source: Wikipedia