1. Sift flour and salt into a mixing bowl.
2. Cut in the shortening and butter into the flour and salt.
3. Dissolve the yeast in the warm water. Once dissolved, stir into the flour mixture along with the sour cream, eggs and vanilla.
4. Cover the bowl with a damp cloth and refrigerate for 2 hours.
5. Roll out half of the dough onto a sugared board into a 8" x 16" rectangle. Return the other half of the dough to the refrigerator.
6. Fold each end towards the center, slightly overlapping them where they meet. Sprinkle the top with sugar.
7. Rotate the dough a quarter turn and roll out again into the same shape. If your dough is sticking to your counter, add more sugar underneath.
8. Fold each end towards the center, overlapping them where they meet and sprinkle the top with sugar.
9. Rotate the dough a quarter turn and repeat the process one more time. This creates layers of sugar in the dough.
10. Roll the dough out 1/4" thick and cut 1" x 4" strips. Twist the ends in the opposite directions, stretching the dough slightly. Shape the twist into a horseshoe and place it on an ungreased baking sheet, pressing the ends down lightly to help them hold their shape. Repeat with the remaining strips of dough.
11. Retrieve the other half of the dough and repeat steps 5-10.
12. Bake the twists at 375 degrees F for 15 minutes, until lightly browned.
13. Remove the twists from the baking sheet immediately and place on a wire rack to cool. Enjoy!