Heat 2 tbsp of oil in a large non-stick pan over a high heat.
Meanwhile, mix flour, salt and pepper in a bowl and lightly coat the beef strips in the flour.
Sear the beef strips in two batches and keep aside.
Add 1 tbsp oil to the same pan, add the mushrooms cooking for 4 minutes or until tender, and set aside.
Add 1 tbsp oil to the same pan, add onion and cook for 3 minutes.
Return the beef pieces to the pan and add in stock and Worcestershire sauce; bring to boil.
Reduce to low heat and allow to simmer till the beef has cooked well and the sauce has thickened enough. Check in between and add more stock if necessary.
Add the mushrooms and season with salt and pepper.
Remove from heat and stir through sour cream.
Serve hot with steamed white rice.