Stir over medium heat 2-1/2 T flour with 1/2 cup milk until smooth and thick.
Cream together 1/2 cup of butter and 1/2 cup granulated sugar. Add to the cooled paste mix, and beat until it’s fluffy. Add 1/2 t vanilla and beat again.
Double recipe if this is for a large sheet cake.
*Joan McBride lived across the street from us in Michigan, and she was a dear friend to my mother!