Preheat oven to 450°. Cut shortening and butter into flour with a pastry blender or fork in a medium bowl until crumbly and mixture resembles small peas. Freeze 10 minutes.
Make a well in center of flour mixture; add buttermilk, and stir with a fork just until dough comes together.
Turn dough out onto a heavily floured surface, and knead 8 to 10 times. Transfer dough to a heavily floured piece of wax paper about 18 inches long. Roll dough into a 14- x 10-inch rectangle.
Spread dough with softened butter, leaving a 1/2-inch border. (Make sure butter is very soft, and spread it gently.) Stir together sugars and cinnamon; sprinkle over butter. Lift and tilt wax paper, and roll up dough, jelly-roll fashion, starting at 1 long side and using wax paper as a guide. Cut dough into 14 to 16 (1-inch-thick) slices. Place rolls in a lightly greased (with cooking spray) 9-inch round pan.
Bake at 450° for 13 to 15 minutes or until rolls are golden brown. Cool in pan on a wire rack 5 minutes.
Meanwhile, prepare Creamy Glaze, and drizzle over rolls.