In a large skillet, melt butter over medium heat. Add mushrooms, onions, and garlic, and cook until tender, about 5 to 7 minutes.
Turn heat up to medium-high and add sliced sirloin. Cook until browned. Stir in flour, followed by consommé, sherry, lemon juice, and pepper, and stir until well-combined.
While your sauce simmers, bring a lightly salted pot of water to a boil and cook egg noodles according to package instructions. Drain and set aside.
Stir sour cream into your beef mixture and heat over medium heat until warmed through. Do not boil or your sour cream may curdle. Salt to taste.