Gather dandelion flowers from a clean, pesticide-free area. Pull off the yellow petals and discard the green parts. Rinse gently and drain until you have about 4 packed cups of petals.

In a medium saucepan, combine petals with 4 cups of water. Bring to a simmer, then cover and let steep for 20 minutes.

Line a sieve with cheesecloth and strain the infusion into a large measuring cup or bowl, pressing gently on the petals to extract all the liquid. Discard the spent petals.

Pour the strained liquid into a large, heavy-bottomed pot. Stir in lemon zest and lemon juice. Sprinkle the powdered pectin evenly and whisk to dissolve.

Bring the mixture to a rolling boil over high heat.

Once boiling, add sugar all at once and return to a rolling boil, stirring constantly. Add the butter to minimize foam.

Boil hard for 1 to 2 minutes while stirring. To check if it’s ready, chill a small spoonful on a plate; if it gels slightly after a minute, it’s ready.

Ladle hot jelly into sterilized jars, leaving 1/4 inch headspace. Wipe rims, apply lids and rings, and process in a boiling water bath for 10 minutes.

Let cool undisturbed. The jars will pop as they seal.