There is some debate in the
mathematical world about who the inventor of
Calculus is.
Archimedes,
Fermat, and
Descartes all made important contributions to the field, but they weren't nearly as formalized as
Newton and
Leibniz. Ask a mathematician who created Calculus, and they will definitely say either Newton or Leibniz. But why isn't there a clear concensus?
It's pretty simple actually. Newton probably discovered it before Leibniz, but he did not publish anything until his later years, and his notation wasn't quite as good as our modern notation. Leibniz, on the other hand, had a very good notation (so good, in fact, that we still use something very close to it to this day, but there is some debate about it), and he published his stuff before Newton. Basically, they both made significant leaps in both the theory of Calculus and its applications, in their own ways.
What does all of this have to do with the "Choco Leibniz"? We've all heard of the popular cookie/cake called the "Fig Newtons". Supposedly, this cookie was named after both Newton the Physicist/Mathematician and the town Newton, Massachusettes. So one of our major Calculus inventors has a cookie with his name.
Another not-so-popular cookie is called the "Choco Leibniz". It is a German cookie (so I'm guessing that is why it isn't so popular here in the U.S.), and it consists of some form of chocolate (either dark chocolate or milk chocolate) covering a butter cracker. One can order these from Germany if one is so inclined. Technically, there is a whole series of Leibniz cookies, but I personally have only seen or tasted the Choco Leibniz.
While I can only speak for their popularity in the United States, it should be fairly obvious that Newton is generally held in higher regard than Leibniz, both because of his extensive studies in many fields, and because his cookie is so much more popular.