I recently just checked on how efficient my food production were on my Capital, I checked the description and got surprised when I saw "Empress" as my Ruler title.
I really thought I had messed up, but then I checked the Government tab, and it said "Emperor".
I have no idea whether or not this was just a One time deal, but it really surprised me.
I have no idea how to replicate it, but can suggest a method:
Create Empire using a male leader.
Ensure that your agenda or ruler traits are food biased.
Check the food yield on planet.
Result!
Pictures:

I really thought I had messed up, but then I checked the Government tab, and it said "Emperor".
I have no idea whether or not this was just a One time deal, but it really surprised me.
I have no idea how to replicate it, but can suggest a method:
Create Empire using a male leader.
Ensure that your agenda or ruler traits are food biased.
Check the food yield on planet.
Result!
Pictures: