1In 3-quart saucepan, cook pasta as directed on package-except add mushrooms, broccoli and carrot during the last 4 minutes of cooking.
2Meanwhile, in 1 1/2-quart saucepan, mix milk, cornstarch, tarragon, salt and garlic. Cook over medium heat, stirring constantly, until mixture thickens and boils. Stir in remaining ingredients until cheese is melted and spinach is wilted. Drain pasta mixture; toss with sauce.