Lightly score ham in diagonal lines first one way, then crosswise, to form a diamond pattern, being careful not to cut any deeper than about a eighth of an inch. (You can score both sides if you like).
Make a paste of brown sugar and mustard (I used Boar's Head Honey Mustard).
Rub paste into ham on sides that have been lightly scored.
Transfer to crock pot.
Pour in two cans of coca cola into bottom of pot, not pouring directly over ham to wash away brown sugar paste.