This article is about the cupcake used for Orange's birthday. You may be looking for Cupcake (Season 5).
The Cupcake was a failed murder weapon that appeared in Happy Birthday. Midget Apple was placed inside it to surprise Orange on his birthday. Midget Apple stayed inside the cupcake until it caught on fire. Midget Apple would have suffocated if Orange and Pear hadn't blown frosting off. However, They accidently blew the frosting onto Marshmallow.