Peel the bananas and put them in a tall saucepan. Add enough water to just cover the fruit. Add lemon juice, puree everything and place on the stove. Set the stove to the highest setting until it boils. Now add the extra sweetness. Mix well and continue to cook.
Halve the heat and simmer for at least 20 minutes.
If the liquid has significantly reduced, twist-off bottles can be filled.
Goes with other fruits too. Since these are pureed, they do not have to be passed through a cheesecloth or something similar. Cherries and the like please stone beforehand.