Fascinating! At first I thought this couldn’t possibly be real, but apparently it is. I found a couple of original newspaper articles about it (here and here) on Google News which are quite interesting.
The entire function would have occurred without notice had it not been for the presence of a photographer from the prestigious Harris & Ewing Studio. What triggered the controversy was a picture that the commander of the Task Force, Vice Admiral William H.P. Blandy, and his wife posed for with Rear Admiral Frank J. Lowry. In it, the so-called “Atomic Admiral” is seen cutting into an elaborately engineered “mushroom cloud”-topped cake (with token assistance from Mrs. Blandy) while Lowry looks on with a smile. The unusual pastry was there in the first place because of an order to an East St. Louis, Illinois bakery by Lieutenant John T. Holloway, a member of Blandy’s staff. “It was strictly a business request,” said Eugene Kuehn to the Associated Press at the time. Kuehn, with the help of a bakery supply salesman named L.Y. Stephens, designed the strange looking dessert and had it delivered by car to Washington.[