Mix flour, powder, salt, soda in bowl. With pastry blender, cut in butter.
Whisk milk and sour cream in small bowl until smooth. Add to flour mixture; stir just until dough forms. Knead if necessary to mix. Shape into disk. Wrap in plastic wrap; refrigerate at least 30 minutes, up to 2 hours.
Heat oven to 425 degrees F. Coat large baking sheet with cooking spray.
Roll dough out on floured surface 1/2-inch thick. Cut out biscuits with 2 1/2-inch cutter. Place on baking sheet. Reroll scraps; cut.
Bake in 425 degree F oven 12 minutes, until golden brown. Serve warm. Makes about 16 biscuits.