1. Stir together first 3 ingredients in a 1-cup glass measuring cup; let stand 5 minutes.
2. Stir together flour and next 4 ingredients in a large bowl; cut butter and shortening into flour mixture with a pastry blender or 2 forks until crumbly. Add yeast mixture and buttermilk, stirring just until dry ingredients are moistened. Cover with plastic wrap, and chill 2 to 72 hours.
To make ahead: Prepare recipe as directed. Cover and chill up to 72 hours. Use as directed in Caramel-Glazed Monkey Bread or Chocolate Rolls.