Preheat oven to 350°. In a 6-qt. stockpot, cook macaroni according to package directions., Meanwhile, in a large saucepan, melt butter over medium heat. Stir in flour until smooth; gradually whisk in milk and mustard. Bring to a boil, stirring constantly; cook and stir 1-2 minutes or until thickened. Stir in jalapenos and 3 cups cheese until cheese is melted., Reserve 1/4 cup crumbled bacon; stir remaining bacon into sauce., Drain macaroni and return to pot; stir in cheese sauce. Transfer to a greased 13x9-in. baking dish; sprinkle with remaining cheese and reserved bacon. Bake, uncovered, 8-10 minutes or until cheese is melted.