The chopped mushrooms are optional. I know this is a substitute for cream of mushroom soup, but I've made it with and without the mushrooms and can't tell a difference in the final casserole. In a medium saucepan, melt 3 tablespoons of butter. Add flour and cook 1 minute. Add salt, pepper, and mushrooms (if adding) and stir. Stirring constantly, add milk or stock and bring to a low boil. Reduce the heat and simmer 3 to 4 minutes or until the mixture thickens slightly.You'll use this entire mixture, OR you can use 1 can of cream of mushroom soup.
3 tablespoons butter, 3 tablespoons all-purpose flour, ¼ teaspoon salt, ⅛ teaspoon black pepper, 1 and ½ cup whole milk, 2 tablespoons mushrooms
Casserole
Pre-heat oven to 350°F and grease a 9x13 baking pan.
Cook the pasta according to package directions, minus two minutes. Drain and return them to the pot.
½ pound pasta
In a large skillet over medium heat, heat the olive oil until shimmering. Add the onion and cook until softened and translucent. Add the beef and garlic and cook thoroughly, breaking up the meat into crumbles with a wooden spoon. Drain if there's too much grease for you. Pour over the cooked pasta.
Stir in the substitute for cream of mushroom soup (above), tomato soup, and milk. Season with salt, pepper, paprika, red pepper, and Italian seasoning to taste. Transfer to the prepared baking pan.
½ teaspoon paprika, ¼ teaspoon red pepper, salt and black pepper, ½ teaspoon Italian seasoning, 1 cup whole milk, 1 can tomato soup