Gather dandelion heads from pesticide-free areas. Pluck the yellow petals from the green base and rinse them gently in cool water.

Spread the petals on a towel to drain.

In a medium saucepan, combine petals and water. Bring to a simmer, then lower heat and let steep, covered, for 15–20 minutes.

Strain the liquid through a fine mesh strainer lined with cheesecloth into a bowl, pressing gently to extract all the liquid.

Pour the dandelion liquid back into a large saucepan. Stir in butter (if using) and pectin, whisking to dissolve.

Bring to a boil over medium-high heat, stirring constantly.

Add sugar all at once and return to a full rolling boil while stirring vigorously. Then add lemon juice.

Continue boiling for 1–2 minutes after the sugar dissolves.

Remove from heat and skim any foam from the top. Ladle hot jelly into hot sterilized jars, leaving 1/4 inch headspace.

Apply lids and process in a boiling water bath for 5 minutes.

Allow jars to cool upright on a towel, listening for the ping of sealing lids.