In a large skillet, heat olive oil over medium heat. Add ground beef and chopped onion, browning the mixture until the beef is no longer pink, about 5-7 minutes. Drain excess fat and season with salt, pepper, tomato paste, and minced garlic. Cook for an additional 2-3 minutes until fragrant.

While the beef is cooking, bring a large pot of salted water to a boil and cook the egg noodles until al dente, about 7-9 minutes. Drain the noodles and set aside to cool slightly.

In a mixing bowl, whisk together sour cream, softened cream cheese, and cornstarch until smooth and well combined.

In a large mixing bowl, combine drained egg noodles, cooked beef mixture, and cheese sauce. Gently fold until evenly coated.

Preheat the oven to 350°F (175°C). Grease a baking dish and layer half of the noodle mixture in the bottom. Sprinkle half of the shredded cheese on top. Repeat with remaining noodle mixture and cheese.

Bake uncovered for 25-30 minutes until the cheese is melted and bubbly.

Let the casserole cool for a few minutes before serving.