Whisk the flour, baking powder and salt in a medium bowl.
In a large bowl, cream the butter, Crisco and sugar until it's light and fluffy. Then cream in the gelatin. Beat in the eggs one at a time, making sure each is well-incorporated. On low speed, mix in the vanilla and pineapple juice.
On low speed, gradually blend in the dry ingredients until just combined. Cover and chill in the refrigerator for at least one hour. (You can also chill the dough overnight.)
Roll out half of the chilled dough onto a floured surface until an 1/8- to 1/4-inch thick. Keep the rest of the dough in the refrigerator until you're ready for it. Use cookie cutters to cut out shapes and transfer them onto a baking sheet lined with parchment paper or a silicone baking mat. Don't put more than 12 cookies on a pan.
Re-roll the scraps until you've used up the dough and then roll out the remaining chilled dough.
Chill each sheet of cookies for at least 30 minutes before baking. Preheat the oven to 375°F (190°C). I don't even preheat the oven until the cookies have been in the fridge for 30 minutes. Bake the cookies (one pan at a time) for no more than 6-7 minutes. Don't worry if they still look a little soft when you take them out of the oven. (But you don't want them to look wet and doughy.) Thicker, larger cookies might need 7 minutes, and smaller cookies will only need 6.
Leave the cookies on the baking sheet for 5 minutes before transferring them to a wire cooling rack.