Problem with homemade butterscotch sauce
I am attempting to make a frozen butterscotch drink but am having problems. My butterscotch sauce recipe is as follows:
1/2 cup butter
1 cup brown sugar
1 cup cream
1/4 cup corn syrup (to help with crystallization)
I melt the butter in a saucepan, add the brown sugar and cold cream, then boil 6 minutes before killing the heat and adding the corn syrup. I let this cool (and even sticking it into the freezer results in no crystallization or problems). My current issue is making it into a frozen drink. I let the caramel sauce cool to warm before adding about 1 quart each cold coffee and cold milk, but after I put this into the freezer I get a layer of butter on top of my frozen coffee. Am I doing something wrong? Why is my caramel sauce is stable by itself but breaks when I try to integrate into a frozen drink base? The texture of the sauce is wonderful and never grainy, but butter separation is a constant. Do I need more corn syrup or some sort of stabilizer/emulsifier? Should I use a different buttetscotch recipe, perhaps? Am I just using too much butter/fat? Or could it be I am shocking the mixture when I add cold cream? This only happens to my sauce when it is mixed in a base of milk or coffee in the freezer, not when it is in the freezer by itself.
Thank you for all your help!