Madame Schwartzhead is a lady opera singer who appeared on Sesame Street.
In one sketch, she sings solo about how whenever she doesn't know a certain word, she sounds it out until she blends it together to form the word sound instead of asking Bob, Big Bird, or the Count to tell her what it says. Unfortunately, her concert goes awry when her loony backstage manager misinterprets what he hears. (SSvideo)
In another sketch, she sings about front and back to the tune of "The Blue Danube," with Pumpkin, Green, and Purple Anything Muppets as back-up singers. In that sketch, her voice is performed by Marilyn Sokol. (YouTube)