Right click on the Desktop.
Left click on New > Shortcut.

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In the Type the location of the item: textbox enter
%windir%\System32\shutdown.exe -s

The -s parameter is used to shut down the computer.

The following two parameters can be used with -s:
-f Forces running applications to close without warning.
-t xx Set timeout for shutdown to xx seconds.

The following command would shut down instantly.
%windir%\System32\shutdown.exe -s -f -t 00

Click the Next > button.

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In the Type a name for this shortcut: textbox enter
Shutdown My Computer (or some other name of your choice)

Click the Finish button.
More Info:
http://www.webtechgeek.com/How-to-on...own-button.htm

This creates a shutdown shortcut on your desktop that requires one click.