Cut the lemon into round slices and pour 4 1/5 cups (1 L) boiling water over them. Add the well washed and drained dandelion flowers.
Let the mixture sit for 6-7 hours, then strain it and put it on the stove to come to a boil with 2 lb (1 kg) sugar.
Boil the mixture to the desired consistency, add 1 tbsp vinegar. Distribute it into jars, boil to vacuum seal them well. Another option is to invert them with the caps down, while still hot. That way they vacuum seal themselves.
Dandelions contain natural rubber. The Latin name for the plant comes from Taraksis - eye inflammation, because dandelions were used to treat it.