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";
?>