Cut the stems off the jalapenos, remove seeds (for milder jalapenos), and slice.
Cut the onion rings in half or fourths depending on the size.
Add the sugar and vinegar to a heavy saucepan.
Bring to a rolling boil, stirring constantly until the sugar is dissolved.
Turn the heat down and simmer the mixture for 5 to 10 minutes, or until it reduced by about half.
Continue to simmer until the temperature reaches about 225F or the syrup thickens when dropped on a cold plate.
Remove from heat.
Carefully add the tequila, jalapenos, and onion.
Return to heat.
Simmer for about 5 minutes, stirring once in awhile to make sure the syrup isn't scorching. If it seems too thick add a tablespoon or two of water.
Remove the pan from the heat.
With a slotted spoon add the jalapenos to a clean jar.
Carefully ladle in the syrup to cover the jalapenos.
Store tightly covered in the refrigerator for at least 24 hours before using.
sliced sweet red peppers may be added in place of the onion. Or use both.
Wear food safe gloves to protect your hands!
Choose fresh, firm jalapenos with no bruising or soft spots.
Although some people can theirs I prefer to make them and keep them in the refrigerator. If you want to can them be sure to read this info on processing times by the National Center for Home Food Preservation.
Some recipes use just the peppers, sugar, and water. I don't care for those because the flavor is too flat. The vinegar and onion add a nice contrast of flavors that keeps them from being weirdly sweet.
I add onions because I like the color contrast, for Christmas I'll add slices of the small red sweet peppers. That adds both a taste and a color contrast.
You can control the spicy heat to some extent by removing the seeds and membrane before you begin for milder peppers. Leave the seeds in and it's going to be infused with the fires from hell. It's your call.
Save any leftover syrup to use in cocktails and sauces. Ok. Mostly cocktails. :) I love a good pineapple margarita made with a splash of this syrup. I also like it on biscuits but that's another story.
Use gloves! I don't use gloves when I'm working with hot peppers but don't do as I do, do as I say and wear gloves. This is especially important if you have sensitive skin.
Don't rub your nose or eyes, and for goodness sake don't go to the bathroom without washing your hands really well beforehand -- and after, of course. Trust me on this.