Preheat oven to 350°. Cook sausage and garlic in hot oil in a large skillet over medium-high heat 5 to 7 minutes or until sausage crumbles and is no longer pink. Remove with a slotted spoon, reserving drippings in skillet. Drain sausage mixture on paper towels, and transfer to a medium bowl. Stir marinara sauce and 1/2 tsp. salt into sausage mixture.
Sauté onion and next 3 ingredients in hot drippings 5 minutes or until tender; stir in olives and chopped pepperoni. Reserve 1/4 cup onion mixture.
Prepare pasta according to package directions in a large Dutch oven.
Melt butter in a heavy saucepan over low heat; whisk in flour until smooth. Cook, whisking constantly, 1 minute. Gradually whisk in half-and-half; cook over medium heat, whisking constantly, 7 to 10 minutes or until mixture is thickened and bubbly. Stir in fresh mozzarella cheese, Parmesan cheese, pepper, and remaining 1/2 tsp. salt. Pour sauce over pasta in Dutch oven, stirring to coat. Stir in onion mixture.
Transfer pasta mixture to a lightly greased 13- x 9-inch baking dish, and top with sausage mixture, packaged mozzarella cheese, reserved 1/4 cup onion mixture, and pepperoni slices.
Bake at 350° for 30 minutes or until cheese is melted and lightly browned. Let stand 5 minutes before serving.
The main idea of this was good--the creamy noodles under the layer of meat and cheese, etc. But the pepperoni, I thought, didn't quite go with the dish. The first time I made this I'd gotten the recipe from somewhere else and used a combination of hamburger and sausage in the meat layer and left out the pepperoni. I used thicker than usual spaghetti on the bottom layer and increased the amount of sauce a little. It turned out just delicious. Maybe I just had beginner's luck on the first one, but I didn't like this casserole as made by this recipe nearly as much.
I made this for church potluck today. I must say it is very delicious and went over very well with everyone. I made with all the recipe ingredients (no more/no less) however not by the recipe instructions. I browned the sausage and garlic in a pot with olive oil. I then added the onion, red/green bell peppers, olives, mushrooms and chopped pepperoni. Once cooked to liking I added the marinara sauce and simmered a bit. I tossed cooked Rotini with the marinara mixture and set aside while I made the white sauce. I made white sauce per instructions except put half & half in marinara jar and shook to incorporate sauce left behind in jar. Once thickened I layered 1/2 of pasta mixture in pyrex pan, topped with 1/2 of white sauce then repeated process. Topped with mozzarella cheese and baked for 45 minutes. I didn't put slices of pepperoni on top, instead I used all pepperoni chopped and added to marinara mixture. Will definitely make again.
Very tasty and filling. Cream sauce really adds a nice touch; almost like a white pizza sauce. I would add some spinach, esp because of the cream sauce. Ingredients take a while to prepare, so if you don't have time after work, prepare ingredients that you can the night before or make it on a weekend. Freeze what you can. Bake this in a traditional lasagna dish. A regular 9X13 pan isn't deep enough. I'm giving this a five because of the taste, but don't consider this a healthy dish.