Prepare the filling. Grease the bottom and edges of an aluminum pan with butter. Place the apricot halves in the pan, alternating them with sugar. Squeeze the lemon juice and pour it over the apricots. Cover the fruit with a towel and leave for 8 hours.
Cook the apricot jam. After 8 hours, put the pan on the fire. Mix the apricots with sugar. Cook over medium heat for 15 minutes. When the sugar dissolves, increase the heat and boil for 20 minutes, stirring occasionally.
Preserve apricot jam. Pour hot jam into jars. Cover with lids, leave until cool, then put in a dark place.