This is one of my favorite soul-warming comfort foods!
In a large skillet, fry bacon. Drain on paper towels. Then crumble and set aside.
In a large soup pot, cook carrots, and celery in water until slightly tender, then add potatoes. (I have found the potatoes get done before the other things if they all go in at the same time.) About 20 minutes. Drain, reserving liquid and set vegetables aside.
In the same pot, cook onions in butter and bacon grease until soft. Then add flour, salt, and pepper. Gradually add milk, stirring constantly until thickened.
Gently stir in cooked vegetables and bacon. Add 1 cup or more of reserved cooking liquid until soup is desired consistency.
Makes 8 - 10 servings. About 2 1/2 quarts.