Mix the flour and water to form a paste and set aside. In a mortar pound together the garlic, coriander root and peppercorns to form a paste. Heat the oil and briefly fry the garlic paste, then add all the remaining ingredients down to and including the sugar, stirring constantly. Add the flour and water paste and stir to thicken. Remove from the heat and leave to cool.
Drain the beancurd sheets and spread out on a flat surface. Place a line of the cooled filling along one edge of each sheet and roll to form a long sausage. Place the 3 sausages in a steamer and steam for 15 minutes. Remove and leave to cool.
When ready to serve, deep-fry the sausages until golden brown, drain and slice into 1/4-inch (6 mm) rounds and serve on a bed of lettuce and mint leaves with Plum Sauce.