Wash fennel; snip 1/4 cup of the leafy tops. Set aside. If desired for garnish, set aside additional leafy tops. Cut off and discard upper stalks of fennel. Remove any wilted outer layers; cut off and discard a thin slice from the base of fennel. Halve, core, and chop remaining fennel. (You should have about 4 cups.)
Combine fennel, potatoes, and broth in a 4-quart Dutch oven. Bring to boiling; reduce heat. Simmer, covered, 15 to 20 minutes or until potatoes are tender. Drain, reserving broth. Set aside in a medium bowl; mash with a potato masher.
Meanwhile, in the same pot, melt butter or margarine over medium heat. Stir in flour, caraway seed, and pepper. Add buttermilk or milk. Cook and stir until slightly thickened and bubbly. Cook 1 minute more. Stir in mashed potato mixture, chicken, and the reserved chopped potatoes, fennel and snipped fennel tops, and broth. Cook and stir until heated through. If necessary, stir in additional broth to achieve desired consistency. If desired, top each serving with Rye Croutons and reserved leafy tops of fennel.
Preheat oven to 300 degrees F. Cut rye bread into 3/4-inch squares; set aside. In a large skillet, melt butter or margarine. Remove from heat. Stir in garlic powder. Add bread cubes, stirring until coated. Spread cubes in a single layer in a shallow baking pan. Bake 10 minutes; stir. Bake 5 minutes more or until cubes are dry and crisp. Cool. Store in tightly covered container up to 1 week.