The most common and most likely answer to this crossword clue is the 6 letter word GRATIN
G
R
A
T
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N
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The straight part
We know that "Cheesy crust" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cheesy crust = gratin.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 GRATIN mean?
GRATIN noun- The top crust of a dish, consisting of breadcrumbs or grated cheese heated under a grill; the dish itself.