Preheat oven to 375°. In a large bowl, cream butter, shortening, sugar and gelatin until light and fluffy, 5-7 minutes. 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. If desired, sprinkle with coarse sugar.
Bake until set (do not brown), 6-8 minutes. Remove to wire racks to cool completely.