In a medium-sized pot, add 6 cups of water (1.5 liters).
Cut off the green parts from the dandelion flowers so it is only the yellow petals left. Remove as much green as possible.
Put the yellow petals in the pot of water.
When all petals are in the water, bring the pot to a boil and stir. Let it simmer for 20 minutes with a lid on.
Remove the pot from heat and let it rest in the fridge for a minimum of 4 hours - preferable overnight.
Strain the dandelion flowers and squeeze out as much liquid as possible. Discard the dandelions.
Add the dandelion liquid, sugar, and lemon juice to a pot and bring to a boil. Let it simmer over low heat for about 1 hour until it has reduced by 50-60%. The longer you let it simmer the thicker syrup it will become.
Add the dandelion syrup to sterilized jars and store it in the fridge. It should keep for about 6 months.