Pick fresh dandelion flowers and gently rinse them if needed to remove dirt or tiny insects. Pat them dry or let them air dry on a towel.
Remove the yellow petals from the green base of the dandelion flower. This takes a little time, but it helps keep the finished syrup from turning bitter.
Place the dandelion petals in a saucepan and pour in the water. Bring the mixture to a gentle simmer, then reduce the heat and let it cook for about 10 minutes.
Remove the pan from the heat and let the petals steep in the liquid for 20 to 30 minutes. For a stronger floral flavor, you can let it steep even longer.
Strain the liquid through a fine mesh strainer or cheesecloth into a clean saucepan, pressing gently to extract as much liquid as possible. Discard the petals.
Add the sugar and lemon juice, if using, to the strained liquid. Stir well and bring it to a gentle simmer over medium heat. Simmer the syrup, stirring occasionally, until it reduces and thickens. This usually takes about 25 to 35 minutes, depending on your pan and heat level. It should look like a thin syrup while hot, and thicken more as it cools.
Pour the hot dandelion honey into a clean jar and let it cool. As it cools, it will thicken into a smooth golden syrup.