GO:0003947:   (N-acetylneuraminyl)-galactosylglucosylceramide N-acetylgalactosaminyltransferase activity
Catalysis of the reaction: UDP-N-acetyl-D-galactosamine + (N-acetylneuraminyl)-D-galactosyl-D-glucosylceramide = UDP + N-acetyl-D-galactosaminyl-(N-acetylneuraminyl)-D-galactosyl-D-glucosylceramide.