1Heat oven to 350°F. Cook and drain macaroni as directed on package, using minimum cook time.
2Meanwhile, in 2-quart saucepan, melt butter over low heat. Stir in flour; cook 1 minute, stirring constantly with whisk. Remove from heat; stir in milk. Heat to simmering; cook 1 minute, stirring constantly, until thickened. Stir in salt, pepper, nutmeg, mustard and pumpkin. Add 1 3/4 cups of the cheese. Cook, stirring occasionally, until cheese is melted.
3Add macaroni to cheese sauce and stir until coated. Pour into ungreased 3-quart casserole. Top with remaining 1/4 cup cheese.
4Bake uncovered 20 to 25 minutes or until golden brown.