A big scoop Della made a mess of (5)
I believe the answer is:
ladle
'a big scoop' is the definition.
'ladle' can be an answer for 'scoop' (as in ladling out scoops of food). I am not certain of the 'a big' bit.
'della made a mess of' is the wordplay.
'made a mess of' indicates anagramming the letters.
'della' anagrammed gives 'LADLE'.
Can you help me to learn more?
(Other definitions for ladle that I've seen before include "Large spoon with long handle" , "Scoop" , "Long-handled spoon for serving soup" , "give out" , "Spoon - a dell (anag)" .)