Get a pot out and pour in the sugar and vinegar. Heat it over medium-high heat

Add the jalapenos and butter to the boiling sugar vinegar mixture. Turn down the heat to medium heat and simmer for 5-10 minutes. Squeeze in the pectin (if you’re using the packet pectin) simmer for about a minute before removing the jelly from the heat.

Pour the hot jelly into your prepared jars*, put (prepared) flats and rings on. Tighten the rings and cool on the counter until the flats pop down and store in the refrigerator for up to 3 months. Or if it’s shelf-stable jelly you’re after, process the jars of jelly for 10 minutes in a boiling water bath.