From the beginning I wanted to include one or tow esolangs.
I quickly decided to give Chef a try because I like the style and challenge of it.
The problem was that the specification of Chef is lacking some basic features like reading arbitrary characters (per specification you can only read numbers).
Therefore, I decided I'd need to create my own Chef parser/interpreter and that was honestly the real challenge. If you're interested in the end product, then check it out :)
None.
As expected, this was a challenge, especially fixing all the bugs in my parser/interpreter.
You also need a lot of unusual approaches due to the limited nature of Chef. For example, there's an infinite number of infinite stacks (at least theoretically) but there's no built-in way to get their length.
At least tomorrow can't really get more complicated ^^