I just put this together from what morty346 posted:
set folder="C:\test"
IF EXIST "%folder%" (
cd /d %folder%
for /F "delims=" %%i in ('dir /b') do (rmdir "%%i" /s/q || del "%%i" /s/q)
)
It adds a quick check that the folder defined in the variable exists first, changes directory to the folder, and deletes the contents.