Preheat the oven to 350°F (175°C).
Cook egg noodles in salted boiling water until al dente. Drain and set aside.
In a large skillet, brown the ground beef and season with garlic salt. Drain excess fat.
Stir in marinara sauce and simmer for 10 minutes.
Mix sour cream, softened cream cheese, and chopped onion in a medium bowl until smooth.
Layer half of the noodles in a 9×13-inch baking dish, top with beef mixture, then add sour cream mixture. Finish with remaining noodles.
Sprinkle grated cheddar cheese evenly over the top.
Bake for 25 minutes or until the cheese is melted and bubbly.
Let the casserole cool slightly before serving.
