A simple solution for walking a nested array to obtain the last set value of a specified key:

<?php

$key = 'blah';
$val = null;
array_walk_recursive( $your_array,
                      function($v, $k, $u) { if($k === $u[0]) $u[1] = $v; },
                      [$key ,&$val] );

echo "$key = $val";

?>