Happy Birthday and Homemade Yellow Cake Mix

September is a Birthday month at our house!  So in honor of these birthdays... this homemade yellow cake mix.  I love that I can make something that I COULD buy in a box... but now I know exactly what is in it and it tastes way better anyway. :)  I follow the substitution she gives for cake flour (since I never have it) and it turns out beautifully.  Enjoy!