How to Eat Politely, 1651

"If thou soakest thy bread or meat in the sauce, soak it not againe, after that thou hast bitten it, dip therein at each time a reasonable morsell which may be eaten at one mouthfull." 

Francis Hawkins, Youths Behaviour 

From the same authority who told you not to be a close-talker, more timeless advice: don't be a double-dipper.