[doneata]

This paper, "Programming by Numbers: A Programming Method for Novices", presents a recipe of how to design recursive functions:

https://eprints.soton.ac.uk/254242/1/p_by_numbers.pdf

And the "The Little Schemer" book has a series of exercises that expose recursive thinking:

https://www.amazon.com/Little-Schemer-Daniel-P-Friedman/dp/0...

Hope this helps!