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/