1) Combine 80ml rum with pear juice and sugar in a 25cm heavy skillet and bring to the boil, stirring occasionally.
2) Reduce heat, add the raisins and pears, and simmer, covered, until pears are just tender, about 10 minutes. Remove the lid from the pan and using a slotted spoon, remove the pears to a plate. Boil the poaching liquid, stirring occasionally, until liquid is reduced to a syrup, 5 to 10 minutes. Stir in the butter and the remaining tablespoon of rum and return the pears to the pan.