1.html.ep

%#= include 'header'; # Does not work
%# layout 'layout'; # Does not work

<%= $callee %> <%= $name %>!
Some text here.

mojo-template-without-include.pl

#!/usr/bin/perl

# skipped

use strict;
use utf8;
use open qw( :std :utf8 );

# skipped

use Mojo::Template;
$template = '1.html.ep';

# skipped

my $mt = Mojo::Template->new->vars(1);

# skipped
my $callee = 'Dear';
my $first_and_middle_name = 'John';

my $out = $mt->render_file($template, {
    'callee' => $callee,
    'name'   => $first_and_middle_name,
});
print $out;