Preheat oven to 350°F. Grease a 13x9-baking dish with butter or nonstick cooking spray.
Bring a large pot of salted water to a boil. Cook egg noodles or pasta according to package directions, 1 minute less than it calls for al dente pasta. Drain and set aside.
Season steak with seasoning salt or salt and black pepper.
In a large skillet over high heat, add ½-1 tablespoon of the butter or oil, enough for a thin layer on the bottom of the pan. Once hot, add steak in one even layer and cook until browned, about 1 ½-2 minutes per side. Don't overcook or overcrowd the pan. Cook in batches if necessary, adding more butter if needed. Transfer to a cutting board.
Once all of the steak has been cooked, roughly chop on the cutting board into bite-sized pieces.
To the same skillet, lower the heat to medium and add 2 tablespoons butter. Once melted, sauté the sliced onions and bell peppers until they are soft, about 5-7 minutes.
Add garlic and cook for an additional 1 minute.
In a large mixing bowl, whisk together sour cream, beef broth, heavy cream, and Italian seasoning.
To the bowl, add the cooked and drained egg noodles or pasta, cooked and chopped steak, vegetables, and American or mozzarella cheese. Mix thoroughly.
Transfer the mixture into the prepared baking dish. Spread it evenly. Sprinkle provolone cheese evenly over the top.
Cover with aluminum foil. Bake 20 minutes. Remove the foil and bake for an additional 10-15 minutes, or until the cheese is melted and bubbly, and the edges are slightly golden.
Remove from the oven and let it rest for a few minutes. Garnish with fresh parsley if desired.