All the research I have done for this points to the same answer as the previous one given: he doesn’t have a favorite food to eat, but he will grill a mean steak to relax after knocking the Joker about Gotham all day.
There’s not a reason given as to why this relaxes him, but some have joked that perhaps the next time someone wants to win against Batman, they just need to line Gotham streets with grills complete with steaks and let him just grill all day and all night long.
Jokes aside, this is as close as comic book lovers can come to knowing what makes the bat-themed superhero smile. We’re simply not given as deep an inside look into his happiness as we are other superheros.
This is actually somewhat interesting to answer. He doesn’t have a favorite food to eat, per say. However, the comic books have mentioned that he loves to grill steaks. That this particular activity helps him relax. As to whether or not this made it into any of the Batman movies, I can’t say; I haven’t seen them recently. Grilling a steak relaxes the bat-themed superhero. He then, presumably, enjoys eating steaks. It’s a higher class meal, especially for the timer period the comics are set in.
As to why his favorite food is a steak, it’s hard to say. It could be something that his parents enjoyed, or something that he thinks that his father might have taught him how to do if they had lived long enough.