That’s a bit of a toughie. Grain gruels are the oldest prepared foods on the the planet. That being the case it stands to reason that rice pudding was first invented in China where rice was first cultivated on a large scale. However if I were to guess I’d say India, which not only has an ancient rice culture, but also an ancient sugar culture. Put the two things together and you have the basis or rice pudding as it’s now known.
What I find interesting about rice pudding is that its use hasn’t changed all that much over the millennia. Yes it’s delicious and nourishing porridge, but it’s also medicinal: good for people with upset stomachs. Ancient Asian and Middle Eastern peoples knew that, as did the Romans and Medieval Europeans, for whom rice was well known as a curative.
Nowadays of course rice is the world’s most widely consumed cereal grain, which means that virtually every culture has a rice pudding they call their own. Some employ eggs, others coconut milk, still others citrus, spices, fruit, nuts, honey, etc.. All are delicious and most are still good for what ails ya…especially after a weekend of over-doing it on rich Thanksgiving fare.