How many letters does the top answer for “author of the scarlet letter” have?

The most common answer is hawthorne (9 letters).

Crossword clue: author of the scarlet letter

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

hawthorne 9 letters wd-fact-v3

United States writer of novels and short stories mostly on moral themes (1804-1864)

moore 5 letters wd-fact-v3

British sculptor whose works are monumental organic forms (1898-1986)

author of the purloined letter 50% similar → poe

author of the screwtape letters 50% similar → lewis

wrote the scarlet letter 50% similar → hawthorne, moore