Remove the core of the quince rubbed with a cloth and cut the pulp into pieces. Peel the pumpkin, scrape out the seeds with the soft inner part and cut the pulp into small cubes.
Put the water, pumpkin pulp and quince in a saucepan. Add the lemon juice and steam everything for about 5 minutes. Then mix with the preserving sugar. Let simmer for 4 minutes. Chop up with a hand blender. Pour into prepared glasses.