The most common and most likely answer to this crossword clue is the 8 letter word STREUSEL
I've seen this crossword clue in The Times
S
T
R
E
U
S
E
L
More clues leading to the result STREUSEL
Buddy explains!
The straight part
We know that "crumble" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case crumble = streusel.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 STREUSEL mean?
STREUSEL noun- A crumbly topping for cakes and quick breads. It is made of sugar, flour, butter, cinnamon, and often chopped nuts.