I used to get this cake from a lady for special occasions but have moved and wish I could figure out how she made it.

She told me that the cake itself was a Betty Crocker White cake mix. But the frosting is what was good. She would store the cake in the freezer because room temperature would cause the frosting to get really soft (similiar to if you let butter sit out for a period of time). She did tell me that she made the frosing primarily out of butter using a roux mixture. I never quite understood what she meant but has anyone heard of this type of frosting?

Thanks!