Preheat the oven to 250 oF / 130 oC. Peel the pears neatly, leaving the stalks on, and stand them in a large casserole. In a saucepan bring the cider, sugar, split vanilla pod and cinnamon sticks to the boil. Pour this over the pears, cover the casserole and bake very slowly for about 3 hours, turning the pears half-way through the cooking time. When the pears are cooked, transfer them to a serving bowl and cool. Pour the liquid into a saucepan, discarding the vanilla pod and cinnamon sticks. Mix the arrowroot with a little cold water to a smooth paste, then add to the saucepan with the liquid. Bring to the boil, stirring till the mixture has thickened slightly to a syrup. Pour it over the pears, allow to cool a little, then baste each pear with a good coating of the syrup. Place in the refrigerator to chill thoroughly and serve sprinkled with toasted flaked almonds and whipped cream.