Place rack in center of oven and preheat to 350°F. Leaving skin on, thinly slice potatoes. Cut stalks and fronds from fennel bulb. Discard stalk. Thinly slice fennel bulb. Chop fennel fronds and set aside. Place potato and fennel slices in 2-quart covered baking dish, and add water to cover vegetables. Cover with lid and microwave on high for about 5 minutes. Let cool slightly and drain vegetables into a colander. Wipe baking dish dry and spray with cooking spray. Add vegetables back to dish and sprinkle with minced garlic. Cut chicken breasts in half (total of four pieces). Place atop the potato-fennel mix. In a bowl, mix melted margarine and flour into a smooth paste. Add 1¼ cups non-fat milk, salt and pepper, stir until smooth. Pour over chicken, potatoes, and fennel. Cover baking dish and place in oven. Bake about 30 minutes. Mix remaining milk with sour cream. Increase oven temperature to 425°F. Remove dish from oven. Spread with sour cream mixture and sprinkle with Parmesan cheese and fennel fronds. Return to oven uncovered and bake an additional 10 minutes until top is golden and bubbling.
United States Potato Board: Potatoes Goodness Unearthed