tasty-recipes-featured-image.php

<?php
/**
 * Uses the post's featured image in the recipe card,
 * if the recipe doesn't have an assigned image.
 *
 * @param array $vars Existing template variables.
 * @return array
 */
add_filter( 'tasty_recipes_recipe_template_vars', function( $vars ) {
	// If there's no image HTML already for the recipe card...
	if ( empty( $vars['recipe_image'] ) ) {
		$post_id = get_the_ID();
		if ( $post_id ) {
			$vars['recipe_image'] = get_the_post_thumbnail( $post_id, 'thumbnail' );
		}
	}
	return $vars;
});