He called his three sons together and he rose up to his feet and declared; "Sons you are all wise and strong but only one of you can rule our precious Vietnam. So, I have devised a plan to determine which of you shall rule after my passing." All of the members of the court and his three sons listening attentively because King Vuong was known to be the wisest ruler in the whole of Asia.

King Vuong continued; "I would like each of you to provide for me a dish of food, you must search for the ingredients and make the dish and serve it to me on the last day of this Lunar Month, and on the basis of this dish I will decide who is to be the ruler of our Kingdom."

Immediately the words had left this King's mouth, the attendants at the court began to talk in hushed whispers. They knew that this was a very wise pronouncement of their King because Vietnam with its large population and small land area must always give attention to food production to make sure that each person is well fed and healthy.

The three brothers stared in disbelief; "How could our father suggest such a method of deciding, why does he not test our strength?" said the first brother. "Why does he not he test our computational skills?" said the second brother. The third and youngest brother just looked at the court and his father and made no comment.

Within days the two elder brothers had organized their servants and horses and carriages and were racing all over Vietnam and even to other parts of South East Asia to find the most delectable and delicious ingredients for the dish. One brother took a boat out into the South China Sea to fish for the finest tasting fish, the other brother went into the Khmer Mountains to find the most tender boar meat. Yet, Prince Tiet Lieu stayed at home and sat on his front step and pondered his father's request.

By the end of the Lunar Month each of the brothers had prepared their dishes and came before the whole of the Vietnamese royal court and their wise father King Vuong to present it. The first brother came to the father and presented a fine porcelain dish of flying fish dressed in a sweet Chili sauce and accompanied by costly lotus seeds. A hush came over the court as the father viewed the dish and placed it on the table. The second brother came forward and he opened a large copper cauldron and presented a joint of boar dressed with wild mushrooms and a rare wild fern sauce. Again all the court watched the father place the cauldron on the table. Then Prince Tiet Lieu came forward and opened his basket and displayed a large flat rice cake. The court and his brothers gasped, no-one would dare offer such simple fare to the royal King Vuong.

King Vuong said, "Prince Tiet Lieu, tell me why you have chosen to present me with such a simple rice cake."

Prince Tiet Lieu said, "Rice is the most precious and valuable of all food found in this Kingdom, yet it is also the most abundant. I have prepared a dish that represents my love for you and our beautiful Vietnam. I have cooked it thoroughly then molded it into a round rice cake, and called it Banh Day as it symbolizes the sky we live under. I have cooked a square rice cake, stuffed it with cooked bean paste and ground meat in the middle and called it Banh Chung. This will symbolize the earth we live on."

As Prince Tiet Lieu spoke his two elder brothers tried to mask the grandness of their dishes as they now understood the wisdom of their younger brother in using ingredients that all the people of Vietnam could have access to. Immediately they fell to their knees in front of their father and younger brother and bowed at the same time the whole court bowed to the father and son as everyone knew that Prince Tiet Lieu would make the finest King to rule after his wise father King Vuong. After that, King Hung Vuong ordered that this recipe be passed out to all people in his kingdom.

As the result, the Vietnamese custom is that every year during the New Year celebration, the Vietnamese people cook Banh Chung and Banh Day and use them as special offerings to their ancestors as well as special gifts to relatives and friends during the Tet celebrations. The Banh Chung is very nutritious, has an original tasty flavor and may be kept for a long time. All of its ingredients and materials, from the green wrapping leaves to sticky rice and pork, green peas and pepper inside, are all medicines (according to Oriental Medicine) that act to keep harmony between the positive and the negative, thus helping the blood circulate well and preventing diseases.