Setup Drupal 9 with acquia BLT
First we will create a Drupal 9 project with the recommended template using the below command.
composer create-project drupal/recommended-project blt-drupal --no-install
This will create a project with the name blt-drupal, since Acquia BLT requires a document root to be docroot, so let's update the project's composer.json file accordingly.