Make the roux by melting butter in a saucepan. Add flour and Knorr Beef Cubes. Continuously stir while cooking for 3 to 5 minutes. Pour water into the saucepan. Stir until all ingredients are well blended. Turn the heat off. Set roux aside.
On a clean pan, heat oil. Saute onion and mushroom until the onion softens.
Add beef. Saute for 3 minutes or until light brown.
Pour-in roux. Stir. Continue cooking in medium heat for 3 minutes. Stir the mixture once in a while.
Adjust heat to low. Add sour cream and season with salt and ground black pepper.
Top over egg noodles. You can also have this with rice or pasta.