In medium pot, over low-medium heat mix the flour and milk together
Stir and cook until thick
Allow to cool
Mix in butter and shortening, beat togehter
Mix in sugar and vanilla
Beat on high speed
Continue until sugar is dissolved then continue to beat for one minute
Notes
This recipe does say to "beat until fluffy" after the butter and shortening are added. The fluffy stage never happened for me. But if it does for you - then maybe it could be used as a frosting.If it doesn't, it still makes an excellent glaze.