Vegetable Casserole

1 medium-butternut squash (about 2 lbs), peeled, seeded, and cut into 1 1/2-inch chunks
3 large red potatoes (about 1 pound), unpeeled and cut into 1 1/2-inch chunks
3 medium-size parsnips, peeled and cut into 1-inch pieces (about 1/2 pound)
1 medium-size red onion, cut into 6 wedges
2 tablespoons olive oil
3/4 teaspoon salt
1/2 teaspoon dried tarragon leaves
1 13 3/4- to 14 1/2-ounce can chicken or vegetable broth
1/2 teaspoon grated lemon peel
1 small bunch broccoli (about 3/4 pound), cut into 2-inch by 1-inch pieces
1/2 cup plus 2/3 cup low-fat milk (1%)
1 tablespoon cornstarch
1 3/4 cups all-purpose baking mix
1/2 cup cornmeal
3/4 teaspoon coarsely ground black pepper

Preheat oven to 450 degrees F. In shallow 3 1/2- to 4-quart casserole or 13" by 9" glass baking dish, toss first 7 ingredients together until well coated. Bake, uncovered, 1 hour or until vegetables are fork-tender and lightly browned, stirring once. After vegetables have cooked 45 minutes, in 3-quart saucepan over high heat, heat broth and lemon peel to boiling. Add broccoli; heat to boiling. Reduce heat to low; cover and simmer broccoli 1 minute. In cup, mix 1/2 cup milk with cornstarch. Stir milk mixture into broccoli mixture,stirring constantly, until mixture boils and thickens slightly; boil 1 minute. Pour broccoli mixture over vegetables; stir until brown bits are loosened from bottom of casserole. In medium bowl, mix baking mix, cornmeal, pepper, and 2/3 cup milk until just combined. Drop 12 heaping spoonfuls of biscuit dough on top of vegetable mixture.Bake cobbler, uncovered, 15 minutes longer or until biscuits are browned.