if you have left it a bit too long…..
place a couple of old towells in the bath, place racks/glass in bath, cover in very hot water, shake in a good lash of washing powder (as in for the washing machine) leaver overnight if you can, lift out racks and give them a run down and rinse off and your good to go.
read this one line after trying oven pride etc and this is the easiest and most effictive way iv tried