FWIW, I've never used a stash before, so my sympathies:). I tried this. Maybe it'll help.

package MyPlugin;
use base qw( Template::Plugin );

use strict 'refs';
use warnings;

sub load {
        my ($class, $context) = @_;
        bless {
                _CONTEXT => $context,
        }, $class;
}

sub new {
    my( $class, $context, $dsn ) = @_;
        
        return $class->error('no stash given')
                unless $dsn;

        bless {
                _DSN => $dsn,
        }, $class;
}

package main;

use strict 'refs';
use warnings;

use Template::Stash;
use Data::Dumper::Concise;

my $stash = Template::Stash->new({ var1 => 'value1', var2 => 'value2'}
+);
print "var1 => ", Dumper( $stash->get( 'var1' )  );
print "var2 => ", Dumper( $stash->get( 'var2' ) );
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