Rinse the blossoms gently and put them in a heatproof bowl or jar. Pour the boiling water over them, cover, and steep in the refrigerator for 12 to 24 hours. The liquid turns deep blue.
Strain out the flowers through cheesecloth or a fine-mesh sieve. You should have about 2 cups of blue infusion.
Pour the infusion into a pot and add the lemon juice. Watch it turn purple. Stir in the pectin and bring to a hard boil. Add the sugar all at once, return to a rolling boil, and boil for 1 minute, stirring constantly. Skim off any foam.
Ladle the hot jelly into clean jars and cap them.
Notes
Refrigerator: Keeps 3 to 4 weeks.Freezer: Keeps up to 6 months.Pantry: For shelf-stable jars that keep up to a year, process them in a boiling water bath for 10 minutes. You don't have to water-bath can it.