Sterilise a 450ml preserving jar (or two smaller ones). Wash them with warm soapy water. Remove all soap residue and let them dry in an 120 degree celsius oven for 15-20 minutes.
Use gloves to slice the jalapeños into rounds. It will seriously sting if you don’t!
In a deep saucepan, combine all the other ingredients together. Bring to a boil and simmer until the salt and sugar have dissolved. Pour in the jalapeños and simmer for 2-3 minutes.
While the liquid is still hot, scoop the jalapeños into the hot clean jar. Pack them down well and top up with the brine until it reaches just below the rim of the jar. Seal and place in a boiling water bath for 10 minutes (if preserving long term.)