During which ruler's reign was the Nimatnama painted, making it a significant example of the Sultanate School of Painting?

Nasir Shah Khalji

Answer:  Nasir Shah Khalji
Nimatnama was painted at Mandu during the reign of Nasir Shah Khalji (1500–1510 CE).

Nimatnama (Book of Delicacies) the most representative example of the Sultanate School of Painting was painted at Mandu during the reign of Nasir Shah Khalji (1500–1510 CE). It is a book of recipes with a section on hunting, and also has methods for preparation of medicines, cosmetics, perfumes and directions on their use. Stories with undertones of Sufi ideas were also gaining favour and Laurchanda paintings are example of this genre.