Brown the beef: Heat a large skillet over medium-high heat and add the avocado oil. Once hot, add the ground beef and begin breaking it up. Stir in the chopped onion and cook until softened. Add the garlic at the very end and cook just until fragrant.
Build the sauce: Stir in the water and beef bouillon and bring the mixture to a simmer. Add half of the salt, black pepper, dried parsley, Worcestershire sauce, and half-and-half.
Thicken: In a small bowl, mix the cornstarch with a splash of cold water to form a slurry. Stir it into the skillet and let the sauce gently simmer until slightly thickened. Taste and adjust seasoning as needed.
Cook the noodles: Add the egg noodles directly to the skillet, stirring to make sure they’re mostly submerged. Cover and cook, stirring occasionally, until the noodles are tender and cooked through.
Finish creamy: Turn off the heat and stir in the sour cream and Parmesan cheese until melted and creamy.
Serve: Spoon into bowls and finish with extra Parmesan and chopped fresh parsley.