Gently rinse dandelion petals under cool water and pick away any green bits. Spread petals on a clean towel to dry.

Combine the petals and 4 cups water in a large saucepan. Bring to a gentle simmer, cover, and let steep for 20 minutes.

Strain through a fine mesh sieve or cheesecloth, pressing gently to extract every drop of floral liquid. Discard the spent petals.

Return the infusion to the pot and measure precisely; add water if needed to reach 3 cups.

Stir in the powdered pectin (if using liquid pectin, follow the product instructions). Bring to a rolling boil over medium-high heat.

Quickly stir in the granulated sugar and return to a full rolling boil that cannot be stirred down. Boil hard for exactly 1 minute, stirring constantly.

Remove from heat and stir in lemon juice and butter to knock down foam.

Ladle hot jelly into sterilized jars, leaving 1/4-inch headspace. Seal with lids and process in a boiling water bath for 10 minutes.

Remove jars, cool on a towel, and listen for the satisfying pop of lids sealing. Let them rest 24 hours before labeling or tasting.