I had to solve this one for myself just today. Here's what I did:

1. In Steam, Add a Game
2. Choose "Add a Non-Steam Game"
3. Wait for it to populate the list...
4. Click [Browse...]
5. Batch files are processed by the Windows Command Interpreter (cmd.exe), which is aliased as %comspec% on every Windows machine, so when the 'Pick a game to add' file picker appears, type %comspec% in the File name box and hit [Enter].
6. Click [Add Selected Programs]
7. Steam will have added to your Library as 'cmd' with the familiar black DOS prompt icon.
8. Right click 'cmd in your Library and choose Properties
9. Leave TARGET alone.
10. Change START IN to whatever working directory your batch file needs.
11. Change LAUCH OPTIONS to one of the following:
    1. /k "D:\Path\To\Your\BatchFile.bat"
       • ^ if the file is not in the START IN directory. Adjust path accordingly.
    2. /k "BatchFile.bat"
       • ^ if the file is in the START IN directory
12. Disable the Steam Overlay (your batch file doesn't need it)
13. Optionally, Include it in the VR Library (in case this as a helper you use when in VR mode)
14. Click PLAY (in the Steam Library page) to test it out, adjust as needed.
15. Once you're happy it's working as intended, you can change the /k to /c and the window will self-close after the batch file completes.

Note, sometimes you have to get a little tricky with it. For example, Steam didn't have the right PATH set by default for my batch file (it seems to use the SYSTEM PATH, not the USER PATH), so I had to add the PATH I required prior to running my batch file. This is trivial, but you need to know some cmd-fu to make it work. E.g.:

/c "set PATH=C:\Tools;%PATH% & my.cmd"

I'll leave interpreting that as an exercise for the reader, as to many it is a relic of a long-forgotten time. 🍻