Preheat the oven to 200°C.
Peel and halve the pears, removing the cores with a teaspoon.
Place pears in a pan with 125g sugar, water, alcohol, lemon juice, and zest.
Simmer the pears for 15 to 20 minutes until tender.
Cool the pears in the liquid, then drain until completely dry.
Gently heat 125g sugar in a pan until golden brown, then stir in 25g butter.
Roll out the pastry and cut a circle slightly larger than the pan.
Place pears cut side up on the caramel and sprinkle with chopped rosemary.
Cover pears with the pastry, tucking the edges down into the pan.
Bake for 15 to 20 minutes until the pastry is golden brown.
Melt 20g butter and chocolate in a bowl over simmering water, then stir in milk.
Stir in the 40g sugar and cream until the sauce is smooth.
Rest the tart for one minute, then invert onto a plate.
Serve the hot tart with chocolate sauce and ice cream.