Select sound, ripe santol. Wash and blanch in boiling water for 10 minutes.
Peel thinly and evenly. Soak peeled santol in cold water.
Cut into halves and remove seeds. Soak in water for three days, changing the water everyday.
Wash santol and blanch in boiling water for 10 minutes. Dip in cold water and drain.
Boil in syrup made up of two parts sugar and one part water for 15 minutes. Let stand overnight.
Boil the syrup again without the santol until thick enough.
Add the santol and continue boiling. Pack in 12-ounces preserving jars and fill with syrup.
Remove air bubbles. Half-seal and sterilize jars in boiling water for 20 minutes. Seal completely.