How can I attach a debugger to a Dancer2 application

Please bear with me, because I don't really know the first thing about Dancer2, other than the fact that I've inherited something written with it.

I want to attach a regular debugger to it, and it's valiantly resisting most of my attempts.

Say I have:

package Wharrgarbl;
use Dancer2;

# lots of stuff

get '/wharrgarbl/:potato' => sub {
  use DB; $DB::single = 1;
  # probably too much code here
}

And I want to be able to attach a debugger to that response handler. How do I complete this incantation?

perl -d -I wharrgarbl/lib -MWharrgarbl -E 'Wharrgarbl->???("/wharrgarbl/fnorb")'