Gently pluck about 4 cups of fresh dandelion petals, avoiding the green parts. Rinse lightly in cold water to remove dirt and bugs.

Place petals in a large pot and add 4 cups of water. Bring to a gentle boil, then reduce heat and simmer for 15 minutes, stirring occasionally.

Strain the infused liquid through a fine mesh strainer or cheesecloth into a large bowl or pot, pressing gently to extract as much liquid as possible. Discard petals.

Return the strained liquid to the pot. Stir in 1/4 cup fresh lemon juice and 4 cups granulated sugar. Dissolve sugar over low heat for about 5 minutes.

Sprinkle pectin evenly over the surface and stir vigorously to avoid lumps. Bring mixture to a rolling boil over medium-high heat. Boil hard for 1-2 minutes, stirring constantly. Add 1 tablespoon butter if desired to reduce foaming.

Test jelly set by spooning a small amount onto a cold plate; if it wrinkles when pushed, it is ready. If not, boil for another minute and test again.

Ladle hot jelly into sterilized jars, leaving 1/4 inch headspace. Wipe rims clean, seal with lids, and let cool to room temperature. Refrigerate or process in a water bath for longer storage.