Makki di roti with sarson da saag is the most emblematically timeless food in Punjab.
Maize is from the Americas. It reached India through the Portuguese and was established as a field crop from around the seventeenth century.
Which means the bread cannot be older than about three or four hundred years. The mustard is ancient. The bread is a colonial-era import that became the emblem of Punjabi authenticity.
This is not a debunking. It is a reminder that the things a place considers immemorial are often quite recent, and that the interesting question about a food is usually when it arrived and what it replaced.
The same applies to most of what is treated as timeless Punjabi food. Chillies, potatoes, tomatoes and groundnuts are all from the Americas and all arrived through the same Portuguese trade. Tea arrived through an advertising campaign in the 1920s and 1930s.
What is actually old in the Punjabi diet is wheat, barley, the millets, pulses, mustard, sugarcane, and dairy in quantity. The millets, which were the staple of the dry Malwa within living memory, are the part that has genuinely been lost.
Makki di roti with sarson da saag is now a winter restaurant dish more than a village one, because Punjab grows very little maize and very little mustard. Both crops were displaced by wheat and paddy for the reason everything else was: procurement.