Preheat the oven to 200C/400F/Gas 6.
Begin by preparing the pears. Peel and halve them, removing the core with a teaspoon.
Put them in a pan with 125g/4½oz of sugar and just enough water to cover. Add the alcohol, lemon juice and zest.
Bring to the boil and gently simmer for fifteen to twenty minutes depending on the ripeness of the pears. Once cooked, test with a sharp knife.
Allow to cool in the liquid. Once cool, remove from the liquid and allow to drain until dry.
Make the caramel by placing 125g/4½oz of sugar into an ovenproof pan. Heat gently without stirring until it turns golden brown. Remove from the heat, add the butter and stir in gently.
Roll out the puff pastry on a floured surface. Cut out a circle slightly larger than the ovenproof pan.
Place the drained and dry pears cut side up in the pan, on top of the caramel. Sprinkle over the chopped rosemary.
Cover the pears and caramel mixture with the pastry, tucking the overlapped edges down the side of the pan.
Bake in the oven for fifteen to twenty minutes until the pastry is brown.
Meanwhile, make the chocolate sauce. Place a glass bowl over a pan of gently simmering water. Melt the butter and chocolate together in the bowl, then stir in the milk.
Add the sugar and cream, stir until smooth, and remove from the heat.
Remove the tart from the oven and leave to rest for one minute before turning it out. To do this, place a plate on top of the pan and invert so that the tart slips out, pastry on the bottom, pears on top.
Serve hot with the chocolate sauce and ice cream.