01 -
Preheat oven to 350°F (177°C). Spray a 9x13-inch baking dish with nonstick cooking spray.
02 -
Heat 2 tablespoons olive oil in a 12-inch skillet. Stir in 1 cup onion and 1/2 cup green bell pepper; sauté over medium heat until translucent. Stir in 1 tablespoon garlic and continue to sauté until fragrant, 1-2 minutes. Add 1 pound ground beef; cook and crumble until no longer pink. Drain grease. Add 1 1/2 teaspoons salt, 3/4 teaspoon black pepper, 1 tablespoon Italian seasoning, and 1 1/2 jars (24-ounce) spaghetti sauce; set aside.
03 -
Cook 16 ounces spaghetti according to package instructions, adding 1 tablespoon salt to the water. Drain.
04 -
In a separate pan, melt 1/2 cup butter. Add 4 cloves minced garlic and sauté on low until fragrant, about 1 minute. Sprinkle 1 tablespoon all-purpose flour over garlic and stir constantly for 1 minute. Remove from heat and whisk in 2 cups heavy cream until smooth. Return to heat, stir in 1 1/2 cups parmesan cheese, and cook gently until melted.
05 -
Add drained spaghetti to Alfredo sauce and toss to evenly coat. Spread coated pasta into the prepared baking dish in an even layer. Top with red sauce without mixing layers. Sprinkle 2 cups mozzarella over the top.
06 -
Bake the dish, uncovered, in the preheated oven until the cheese is melted and the casserole is bubbly, about 30 minutes. Let cool for 10 minutes. Sprinkle with fresh parsley and a pinch of dried Italian seasoning before serving.