Hello! Lots of good suggestions here already.

But I am here to shill for my favourite manga, now being adapted into an anime, Dungeon Meshi.

The first 12 episodes are on netflix and so far the execution has been stellar. I'm running a community for it here: !dungeonmeshi@ani.social

You mention the slow character build up and detailed world building of Frieren being enjoyable, and Dungeon Meshi excels at those same things. Personally I'd even dare say it keeps up the quality of that stuff, while it eventually kind falls off a bit in Frieren in favor of focusing on arcs that can feel like B-plots. That's not even a criticism, it's simply a different kind of story, and the anime hasn't gotten to that point.

Dungeon Meshi in comparison is fairly short (I currently estimate it will wrap up in 48 episodes, after a second season), but it is a deep and complex story featuring far more than one character worth focusing on, set in a world with a rich history. Its rate of publishing was a single chapter every other month, which I think resulted in a level of attention to detail few weekly published mangas can achieve.

It merely masquerades as a simple comedy/cooking story with a fantasy gimmick.

And now we are getting an anime adaptation of that masterpiece, by none other than Studio Trigger!

If you give it a chance, pay attention to the details, as it starts to set things up from episode one, that will come together only much later.