Step 1Combine the peppercorns and allspice in a mortar and coarsely crush with pestle. Place the spices in a large saucepan or pot (wide enough to hold the pears, halved, in a single layer). Add the Port and sugar and bring to a boil. Reduce the heat and simmer 15 minutes.
Step 2While the Port mixture steeps, peel, halve and core the pears.
Step 3Strain the Port mixture through a fine sieve to remove the spices. Return it to the pan on low heat. Lay the pears into the pan, cut side down. Cover and cook over low heat for 5 minutes. Uncover and turn the pears over. Cover and cook 3 minutes longer, until the pears are soft but not mushy. Transfer to a platter with a slotted spoon and arrange cut side up.
Step 4Raise the heat under the saucepan and cook the liquid until it is reduced almost to a glaze, to about half a cup, about 15 minutes. Pour over the pears, filling each cavity, and serve at once or after cooling.