Combine celery, water, tarragon and 1 tablespoon of the butter. Bring to boil; simmer 10 minutes. Turn celery into buttered casserole. Melt remaining butter in same saucepan over medium heat; stir in flour and salt. Stir until well browned. Add milk and cook until thick. Add soup and heat. Add cheese and stir until melted. Pour over celery and toss lightly. Sprinkle with paprika. Bake at 350 degrees for 15 minutes or until bubbly.