Melt the butter in a large Dutch oven or soup pot over medium high heat. Add the mushrooms and sprinkle with a little salt and pepper. Cook until the mushrooms release their liquid and begin to brown, about 8 minutes.
Add the onion and garlic and cook until tender, about 5 minutes. Add 6 cups of the stock and bring to a gentle boil.
Whisk together the sour cream, flour, and remaining 1 cup beef stock in a separate bowl. Add the sour cream mixture to the mushroom mixture. Simmer over medium heat until the soup is slightly thickened, about 5 minutes.
Stir in the Worcestershire sauce and noodles. Simmer for 6 minutes or until the noodles are tender. Stir in the lemon juice, chopped dill, and season with salt and pepper to taste. Ladle the hot soup into serving bowls and garnish with more dill if desired.