Heat the oil in a frying pan over medium heat and stir fry the mushrooms, onion and beef until brown.
Add the water and soup base, then bring it to a boil. Stir well and cook for 2 minutes.
After turning off the heat, add the sour cream. Stir well until the sour cream dissolve into the soup.
In a small pot, bring about 2 cups of water to a boil. Add the Udon noodles and stir until separated. Drain the Udon.
Transfer the Udon to a serving plate and pour the sauce from Step 3. Sprinkle with dried parsley, and you are done!