In a large saucepan cook and stir carrots, celery, and garlic in hot margarine or butter over medium heat for 4 minutes or until tender. Carefully stir in chicken broth, potatoes, and dill. Bring to boiling. Reduce heat and simmer, covered, for 20 to 25 minutes or until potatoes are tender. With the back of a spoon, lightly mash about half of the potatoes in the broth. Stir the beans into the potato mixture.
In a small mixing bowl stir together the sour cream or yogurt, flour, pepper, and, if desired, salt; stir into potato mixture. Cook and stir until thickened and bubbly. Cook and stir for 1 minute more. Makes 4 to 6 main-dish servings.