Use the 'medium' image size for a Tasty Recipe card when it exists.

tasty-recipes-medium-image-size.php

<?php
/**
 * Use the 'medium' image size for a Tasty Recipe card when it exists.
 *
 * @param array  $template_vars Template variables to be used.
 * @param object $recipe        Recipe object.
 */
add_filter( 'tasty_recipes_recipe_template_vars', function( $template_vars, $recipe ) {
	$recipe_json = $recipe->to_json();
	if ( ! empty( $recipe_json['image_sizes']['medium'] ) ) {
		$template_vars['recipe_image'] = $recipe_json['image_sizes']['medium']['html'];
	}
	return $template_vars;
}, 10, 2 );