Soften yeast in the warm water. In a large bowl, whisk together the flour and salt. Use a pastry blender or electric mixer on low speed to mix in the butter and shortening until it resembles coarse crumbs. Beat in eggs, sour cream, vanilla, and yeast mixture, until well combined. Divide dough in half, cover and chill for 2 hours, or until firm enough to roll. Preheat oven to 350 degrees F. Line two cookie sheets with silicone baking mats. In a small bowl, combine the sugar filling ingredients. Sprinkle some of the sugar filling on your surface and roll out one half of the dough to about 16 inches x 8 inches. Sprinkle about 1/4 cup sugar filling on top. Fold one end of the dough over to the center, fold other end over to make 3 layers (like folding a letter). Roll out again. Repeat the sugar filling and folding process, roll out to 1/4-inch thick. Cut into 4-inch x 1-inch strips. Twist and place on cookie sheet, at least an inch apart. Repeat with remaining dough. Bake for 15-17 minutes. Store at room temperature in an airtight container, for up to 1 week. To refresh twists, if needed, place on cookie sheet and reheat at 350 for 5 minutes. Can also be frozen for up to 3 months.