composite type insert

I'm trying to understand how to insert a composite type value.  I'm
having trouble with the last sql statement below.  It errors out with:

ERROR:  cannot cast type record to atype

How should I create a composite type value out of columns a and b in
table tt that I can insert into table atable?

CREATE TYPE atype AS (
  acol
    TEXT,
  bcol
    TEXT
);

CREATE TABLE atable (
  aval
    atype
);

CREATE TEMP TABLE
  tt
AS
  SELECT 'aaa'::text AS a, 'bbb'::text AS b;

INSERT INTO
  atable
SELECT
  ROW(a, b)
FROM
  tt;

Thanks as always.

--
Ron Peterson
https://www.yellowbank.com/