In a large bowl, cream the butter, shortening, sugar and gelatin until light and fluffy. Beat in egg and vanilla. Combine the flour, baking powder and salt; gradually add to creamed mixture and mix well.
Using a cookie press fitted with the disk of your choice, press dough 2 in. apart onto ungreased baking sheets. Decorate with sprinkles.
Bake at 375° for 6-8 minutes or until set (do not brown). Remove to wire racks to cool completely.