Pat dry the beef cubes, and coat them with salt & pepper and corn flour.

In a big pot, add 2 tbsp oil and then add beef cubes and cook for about 5 mins until both side are slightly browny.

Add 2 litre water, tomatoes, onions, carrots, mushrooms into the pot.

Add chicken stock and ketchup into the pot.

On high heat, bring the water to boiling and then turn it down to lower heat leave it for 2 hours.

Taste the soup, add butter or salt if needed.

Prepare your noodles in another pot.

Serve it with bak choy and coriander.