Prepare egg noodles according to package directions. Drain noodles, and set aside.
Cook ground beef, green onions, garlic, and 1/2 teaspoon salt in a large nonstick skillet over medium-high heat, stirring 10 minutes or until it crumbles and is no longer pink. Drain well.
Stir in tomato-basil pasta sauce and pepper. Cover, reduce heat, and simmer 20 minutes.
Stir together egg noodles, mascarpone cheese, 1 cup sour cream, and remaining 1/4 teaspoon salt until blended.
Layer half each of egg noodle mixture and ground beef mixture in a lightly greased 2-quart baking dish. Repeat layers.
Bake at 350° for 25 minutes. Remove from oven; sprinkle evenly with Parmesan cheese, and bake 5 more minutes.
Let stand 10 minutes before serving.
*1 (8-ounce) package cream cheese may be substituted for fresh mascarpone cheese.