Cook potatoes and onions together until potatoes are tender. Drain. Save potato water. Put the potatoes through a ricer or coarse strainer. While potatoes cook, melt the butter in a heavy 6 qt. saucepan. Add chopped parsley and basil. Blend in flour, salt, and pepper; gradually stir in the cold milk. Add scalded milk and potato water. Cook over medium heat; stir in potatoes and onion; heat. Serve in bowl. Sprinkle soup with chopped parsley or dust with paprika.