Birthday !

Donna is an artist. When she decorates a cake it is a work of art. The base frosting is carefully worked to a smooth surface. The writing is calligraphic and surrounded by tastefully arranged, exquisitely formed flowers and other decorative elements. It is almost too beautiful to eat.
Joe is an engineer. When he decorates a cake it is good to eat. (He spells like an engineer too.)
Based on this information, perhaps you can surmise whose birthday we are celebrating.