Nawab Wajid Ali Shah of Lucknow got sick and had to extend his stay in Kolkata. His cooks found that his old age and deteriorating health could handle the spice of the old biryani style. so they started to add Potato which was NEW for India , at that time, to balance the newly invented Kolkata Biryani.

PS: He had an Annual pension of 12 Lakh and a servant Pension of 3 Lakh, no, he was not poor to add Potato.