Rinse jalapeño peppers and remove stems and seeds (you can leave the seeds in if you like it spicy). In food processor or blender, finely chop peppers.
Place peppers in a large pot or heavy large saucepan with vinegar, salt and sugar and bring to a full rolling boil over medium-high heat. Boil for 10 minutes, stirring often.
Add Certo pouch (liquid pectin), stir, and boil 1 more minute. Skim off any foam that forms to ensure a smooth texture in the finished jelly.
Use a canning funnel to fill the sterilized, half-pint, canning jars leaving 1 inch headspace. Use a lightly damp paper towel to wipe the rims of the jars before adding sterilized canning center lids, the screw on the band until just tight, but not completely tightened.
Add jars to a water bath for 10 minutes (follow water bath canner instructions carefully and adjust for high altitude, you may need to process longer). Remove the jars using a canning jar lifter.
Once the jars have cooled, completely tighten the band around the lid. The lids on the jars should pop down letting you know the jars have been safely sealed. Check all the jars and lids before storing. Label the jars with the date to track freshness. Wait a day or so before serving so the jelly has a chance to 'gel' or set.
Serve on crackers with cream cheese. This jelly is also delicious as a dipping sauce for steak or chicken nuggets.