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. This should yield about 3 cups (if you have extra, set aside to use for salsa or any other dish).
Place chopped 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 5 minutes, stirring often.
Start off by only adding 3 ounces of liquid pectin, stir, and boil 1 more minute. Don't add all the pectin in all at once. Skim off any foam that forms during the simmering process to ensure a smooth texture in the finished jelly.Do a spoon test by dropping a little jelly onto a cold plate and letting it sit for 1-2 minutes. If it slowly thickens and moves slowly like thick syrup, it’s ready. If it’s too runny, add a little more pectin an ounce at a time and repeat the test. If it’s too firm and sits on the plate like a blob, stir in a splash of hot water or vinegar before jarring. Use a canning funnel to fill the sterilized, half-pint, canning jars leaving 1/2 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.