Gather all ingredients.
Melt 2 tablespoons butter in a large skillet over medium heat. Add mushrooms and onion; cook and stir until soft, about 5 minutes. Transfer to a bowl; do not clean the skillet.
Fill a large pot with lightly salted water and bring to a rapid boil. Cook egg noodles at a boil until tender yet firm to the bite, 7 to 9 minutes. Drain.
While the noodles are cooking, melt remaining 2 tablespoons butter in the skillet over medium heat. Add ground beef and sauté until browned and crumbly, 7 to 9 minutes.
Mix in flour and cook for 1 minute.
Stir in broth and cook until slightly thickened, 2 to 4 minutes.
Add mushroom mixture, then stir in sour cream, salt, and pepper. Cook, stirring occasionally until sauce is hot, 2 to 3 minutes; do not boil.
