copy NUL EmptyFile.txt
DOS has a few special files (devices, actually) that exist in every directory, NUL being the equivalent of UNIX’s /dev/null: it’s a magic file that’s always empty and throws away anything you write to it. Here’s a list of some others; CON is occasionally useful as well.
To avoid having any output at all, you can use
copy /y NUL EmptyFile.txt >NUL
/y prevents copy from asking a question you can’t see when output goes to NUL.