Bring a large pot of water to a boil. Add 12 ounces egg noodles and cook according to package directions. Drain and set aside.
While the noodles cook, brown 1 pound ground beef in a large skillet over medium-high heat until cooked through, breaking up the meat as it cooks. Drain any excess grease. Set aside.
In the same pot you used for the noodles, combine 15 ounces sour cream, 10.5 ounces cream of mushroom soup, and ¾ teaspoon onion powder over medium-low heat. Cook for 2 to 3 minutes, stirring occasionally, until warmed through.
Keep the heat gentle when warming the sauce. Medium-low is all you need. The sour cream can separate if it gets too hot.
Add the cooked egg noodles and ground beef to the pot. Stir gently until everything is well combined.
Season with salt and pepper to taste. Sprinkle with chopped fresh parsley if desired. Serve warm.
Notes
Use 90/10 ground beef for the best flavor with minimal grease. If you use an 80/20 or 85/15 blend, drain well before combining with the sauce.
The sauce thickens as it sits and the noodles absorb moisture. Stir in a splash of milk to loosen it as needed.
Store leftovers in an airtight container in the refrigerator for 3 to 4 days.