Combine the pears, orange slices, dark brown sugar, cinnamon sticks, whole cloves, vanilla pod and allspice in a large stock pot and cover with about 12 cups of water. You want the water to cover the pears. Bring to a boil, reduce to a simmer and cook for 1 hour uncovered. After 1 hour, the next steps are to pull out about 6 pear halves and mash with a fork; put back in the pot. Cover and simmer for another 2 hours.
Allow the pear mixture to cool slightly. Strain it through a fine mesh sieve to remove the pears, stems, seeds, etc. You can strain it several times, to get the consistency you are looking for.
Keep hot on the stovetop or you can put it into a slow cooker on low heat.
Serve hot with a cinnamon stick and one whole clove and a fresh orange slice.