use warnings;
use strict;
use Data::Dumper;

my %hoh;
$hoh{element1} = {start => 1,
                  middle => 5};

print Dumper \%hoh;

 $hoh{element1}{end}=10;  # add to hash

print Dumper \%hoh;

##</code><code>##

$VAR1 = {
          'element1' => {
                          'middle' => 5,
                          'end' => 10,
                          'start' => 1
                        }
        };