Pick dandelion petals off the stems. Wear gloves to avoid staining your hands. Measure 5 1/2 ounces of petals and discard the stems and leaves.
Transfer dandelion petals to a container and cover completely with water. Cover and steep in a cool, dark place, up to 24 hours.
Drain through a fine-mesh sieve into a saucepan, squeezing petals as dry as possible with your hands. Stir in sugar and lemon juice and bring to a boil over medium heat. Simmer uncovered until a thin syrup forms, about 45 minutes. Cool until syrup thickens slightly.
