Heat a small skillet coated with cooking spray over medium heat.
Add onion; cook 6 minutes or until tender, stirring frequently. Spoon onion into a blender.
Add milk; process until smooth. Cool.
Lightly spoon flours into dry measuring cups, and level with a knife.
Combine flours and next 5 ingredients (flours through basil) in a large bowl; cut in the butter with a pastry blender or 2 knives until the mixture resembles coarse meal.
Add onion mixture; stir just until moist. Turn dough out onto a heavily floured surface (dough will be sticky), and knead lightly 5 times with floured hands.
Roll dough to a 1/2-inch thickness; cut into 10 biscuits with a 3-inch biscuit cutter.
Place on a baking sheet coated with cooking spray.