functions.php

<?php

/**
 * Featured Image on Single Posts
 *
 */
function be_single_featured_image() {
  if( is_single() && has_post_thumbnail() )
    echo '<p class="featured-image">' . get_the_post_thumbnail( null, 'large' ) . '</p>';
}
add_action( 'genesis_before_post_content', 'be_single_featured_image' );