Writer mixed lots in trifle (7)
I believe the answer is:
tolstoy
'writer' is the definition.
(I've seen this before)
'mixed lots in trifle' is the wordplay.
'mixed' indicates an anagram.
'in' means one lot of letters goes inside another.
'trifle' becomes 'toy' (I've seen this in another clue).
'lots' with letters rearranged gives 'lsto'.
'lsto' placed into 'toy' is 'TOLSTOY'.
(Other definitions for tolstoy that I've seen before include "Count Leo . . . . . . . wrote 'War and Peace'" , "Lost toy belonging to Count Leo, writer" , "Lost toy of the Russian author" , "Writer of War and Peace, d.1910" , "Russian writer, 1828-1910" .)