Allow to simmer for up to 2 hours. You will need to gently turn them so that they are cooking evenly in the chocolate sauce. To test if they are done, stick a fork gently inside of the cored pear so that you don't leave marks on the outside. Once they are tender on the inside, remove the pears. Turn up the heat on the pot and cook the chocolate poaching liquid until it thickens, about 10-15 minutes. You want it thick enough to coat the back of a spoon.