tondo circular panel paintings ('tondi'), became popular in Italy about the middle of the 15th century. The word derives from 'rotondo', the Italian for circular.
The National Gallery, UK website

Thirty round oil paintings were produced in ten months' time.  Painted quickly, many are completed in one sitting.  Before beginning Tondo, I was working from memory using egg tempera on rectangular panels, working very slowly, scraping away as often as adding paint.  Since 2000, half the studio time is spent on The Last Supper plates: all those porcelain circles, they influence the Tondo series format.  One day the rectangle suddenly seemed masculine and full of corners.

Having painted for 24 years, I have certain methods, habits and rules.
In Tondo, I am allowed to break the following Julie rules:
You must work from memory, no looking at objects.
No photo references.
No text.
You should spend a certain amount of time on each painting.
The paintings in the series must relate thematically.

In Tondo, I paint whatever I wish.