Into a pot, bring to boil beef cubes with 2 1/2 L water, seasoned with salt and white pepper. Add in sliced onion.
When beef is half soft, add in vinegar
Once beef completely soft, make roux, then stir in roux into pot, followed with liver
Adjust flavor and cook only for 3-4 minutes long
Serve immediately (with any kinds of pasta you prefer) with a dollop or two of sour cream. Enjoy~