Stem the pears and cut them into quarters lengthwise. Leave the skins on, but trim away any dark spots or bruises. Core them and divide the quarters in half again lengthwise, so you wind up with 8 pieces from each pear.
In a wide saucepan or deep skillet, combine the wine, juice, cinnamon, allspice, and optional cloves. Bring the mixture to a gentle simmer. Cover and simmer over low heat until the pears are tender but not overdone, stirring occasionally. The time this takes depends on the ripeness of the pears, but aim for 10 to 15 minutes or so, and test with a small fork occasionally.
Once the pears are done, dissolve the arrowroot or cornstarch in just enough water to liquify it, and drizzle into the gently simmering liquid in the saucepan, stirring all the while. It should thicken up immediately. Remove from the heat.
Cover the pan and allow to stand until just warm or at room temperature. To serve, divide among small plates or shallow dessert bowls. Divide the wine sauce among the servings. Accompany with your favorite dark chocolate, if you'd like.