My brother made a chocolate cake (from scratch) and baked it in a heart-shaped cake pan.  He frosted the cake with homemade frosting and frosted a keyhole out of a different colored frosting in the middle of the cake.  He then bought a large Hershey bar (the kind that is really big and really thick) and cut it into a key shape.  He gave both of these to his girlfriend with a note that read "you are the key to my heart".