Peel the apples and cut into pieces. Add the lemon juice, the preserving sugar and the rosemary sprig to the apples and stir. Cover and let the apples stand for a while, e.g. overnight. For impatient people like me, 1-2 hours are enough. Bring everything together in a saucepan to the boil while stirring and cook for 5 minutes. Then remove the rosemary sprig. Now the jam can be pureed as you like, or it can not be poured into glasses while hot. I put a small sprig of rosemary in each glass as a decoration.