The most common and most likely answer to this crossword clue is the 5 letter word RARER
I've seen this crossword clue in The Guardian
R
A
R
E
R
More clues leading to the result RARER
- Less common instalment of Frasier, a rerun
- Painter stern after spilling a thinner on the ground
- Painter behind spilling first rate thinner on the ground
- Army groups initially return more bloody
- Comparatively sparse portion of land fenced off by Bishop
- Less widely known rule on poison copper ignored
- Recipe in back reviewed and not cooked so well
- In summer are roasts not cooked as much?
- More uncommon gaps a European fills in basic education
- Turning back, receiving resistance is less common
Buddy explains!

The straight part
We know that "not cooked so well" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case not cooked so well = rarer.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does RARER mean?
RARER adjective- Very uncommon; scarce.
- (of a gas) Thin; of low density.
- Good; enjoyable.
- (particularly meats) Cooked very lightly, so the meat is still red (in the case of steak or beef in the general sense).