There are a gazillion of papers like that. Actually, that's how this lowly talking duckling roles when not proving mathly-hardcore theorems.

Where to submit depends on the nature of your paper. You may have to adjust your writing style and even change the content to an extent. Either way, the golden rule I learned from my advisor and postdoc mentors is that you write your paper for your target audience and submit where they do research.

Since shiny papers by great researchers like nobel laureates may not be extremely practical examples your average guy can easily reproduce, here are how I usually do, just so you know there are a lot of mediocre examples like that too. (No. This is not a shameless self-promotion of my papers. Honest!)

A typical example of things like what you described happens when you find an equivalence between a well-studied math object in your field and something that's seemingly unrelated in another field. For example, I was reading this paper published in Science about how you can exploit Bell pairs to correct the effect of decoherence for quantum communication and another paper by the same authors published in Physical Review A about how that idea and state-of-the-art coding theory may go together. I also did a serious amount of research on this myself and actually published one paper. But after a while, I suddenly realized that what we'd been looking at is, after all, exactly the same as a fundamental class of combinatorial designs (with some caveat in fine print which I omit).

With this equivalence, I was able to import known classical results in design theory; I described what kind of quantum code their method must end up with and gave bounds on code parameters and whatnot without really proving anything except the equivalence. In this case, the target audience was coding theorists, design theorists, and physicists who read said two papers. So I chose the journal that has exactly this audience (which was IEEE Transactions on Information Theory if anyone is curious).

I could submit it to some physics journal, but such a journal wouldn't attract coding theorists and design theorists; the point of my paper was to show an example of how design theory, coding theory, and quantum error correction interact. A specialized combinatorics journal wouldn't be the best choice either because that's not where quantum physicists usually come. So I picked a journal that has a dedicated section for quantum information and is read by both mathematicians and electrical engineers. Incidentally, the editor asked us to translate some part of the original manuscript into the language of coding theory, so it's important to consider what the majority of the journal's audience is familiar with.

You can still do serious mathematics too if you like even if you just found an equivalence or new application of known math. For example, when I was a grad student, I was given a design theory problem that an engineer at nVidia brought to my mentor. I got curious about the computer engineering behind it, and I found out that the problem actually stems from a more general VLSI testing technique which Intel developed years ago. And I noticed that this general version can be understood as a problem of finding a linear hash function with certain nice combinatorial properties.

This combinatorial problem got me, so I formalized the technique Intel used to use and did purely combinatorial research. The direction of research I took and the results I got was too math-centric, so my paper wouldn't be extremely attractive to people making money in real life off of the kind of computer engineering I did some math about. But I couldn't help it because I got more interested in the math problem I defined by (obviously overly) generalizing the original engineering problem. So I wrote my paper the way (applied) discrete mathematicians would do, and submit it to a very mathematical journal that also deals with electrical engineering.

One thing you might want to note is that such papers may take longer to get published. For instance, editors may have hard time finding appropriate referees. If you're connecting two fields, the editor may need someone who speaks two previously unrelated subfields or find it difficult to convince potential referees that they can understand and judge your manuscript; your paper may look frightening at first glance to a potential referee who only knows one of the two fields well. And if your paper does require a substancial amount of knowledge in two fields to check validity and judge its quality, you don't expect your referees would return their reports in a month.

In any case, there are a lot of examples like your case. And it doesn't need to be an all-time-most-cited paper either. After all, if you're doing mathematics that you find cute and interesting, chances are someone in a different field was/is/will be thinking about a similar thing in a different scientific language. And pure math shines when you find such relations because of its rigor and generality.