Preheat the oven to 200°C, 400°F, Gas 6.
Split the peaches in half and take out the stones. Make four parcels out of either dampened greaseproof paper or a double layer of foil and place the peaches in the middle.
Dot the hollow of each peach half with a little butter, some of the alcohol, a little lemon juice and sugar and top with rosemary. Enclose the parcels tightly and bake in the oven for 10-12 minutes until tender.
Open the parcels at the table and serve with your choice of accompaniment.