Mash with a potato masher. Let mash stand in a sieve for a few minutes to drain more liquid off.
Put in a large microwave-safe bowl or jug.
Add remaining ingredients and mix.
Zap in microwave for about 5 minutes.
Serve piping hot.
Notes
Option: Add a drained jar of turnip or parsnip; won't affect nutrition significantly.Instead of low-fat sour cream, you can use low-fat yoghurt.Play with seasoning, of course, as desired. The rosemary adds a nice warmth. Whole unground rosemary leaves, though, can be abrasive in this mixture.Freeze the broth you drain off the jars to use in soup.