Fast Food Franchise question pleaasseee help?

You can use any example you like Mcdonalds(ew) Burger king(ew) or anything like that. But I want to open a Baskin Robbins. Lets say i do this, would i be able to use the ice cream to make a certain dessert of my own creation? Like a Christmas Sundae. Or would this be like illegal and the buisness HQ doesn't allow this to happen?