What is the total number of production code listings of episodes written by Matthew Lau?
CREATE TABLE "table1_27116696_1" (
  "no_in_series" real,
  "no_in_season" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "production_code" text,
  "u_s_viewers_million" text
);
SELECT COUNT("production_code") FROM "table1_27116696_1" WHERE "written_by"='Matthew Lau';