If it's only slightly burnt an hours soak in strong salt water will do the trick, but if it's really caked on it may need as long as 12 hours with a boil-up before and after.
If required repeat last part until sugar is gone.
Further to an earlier answer - pop a dishwasher tablet in the pan, fill with water and leave overnight. Use this for all "Burn ons". I know I've been there"!!