Step 1: Preheat your oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish.
Step 2: Heat olive oil in a large skillet over medium-high heat. Add ground beef and diced onion. Cook, breaking up the beef, until browned and the onion is softened, about 6-8 minutes. Drain any excess fat.
Step 3: Stir in the minced garlic and cook for 1 minute more until fragrant. Add the diced tomatoes (with their juice), tomato sauce, Italian seasoning, salt, and pepper. Bring to a simmer, then reduce heat and let it cook for 5 minutes, allowing the flavors to meld.
Step 4: While the beef mixture simmers, bring a large pot of salted water to a boil. Add the egg noodles and cook according to package directions until al dente (slightly firm). Drain well.
Step 5: In a large bowl, combine the cooked egg noodles, milk, and sour cream. Mix gently until the noodles are evenly coated.
Step 6: Spread half of the sour cream noodle mixture evenly into the bottom of the prepared baking dish.
Step 7: Spoon the entire ground beef mixture over the noodles in the baking dish, spreading it out evenly.
Step 8: Top the beef layer with the remaining sour cream noodle mixture, spreading it gently to cover the beef.
Step 9: Sprinkle the shredded cheddar cheese and mozzarella cheese evenly over the top layer of noodles.
Step 10: Bake for 25-30 minutes, or until the casserole is bubbly around the edges and the cheese is melted and lightly golden. If desired, you can broil for the last 1-2 minutes for a crispier, golden-brown topping (watch carefully to prevent burning).
Step 11: Remove from oven and let stand for 5-10 minutes before serving. Garnish with fresh chopped parsley if desired. Enjoy your ultimate comfort food!