Using a sharp knife, cut the jalapeños into 5mm thick slices, discarding the stem. Set to one side.I'd recommend wearing a pair of gloves to do this! Next, add the vinegar, sugar, peppercorns, garlic granules & cayenne pepper into a medium saucepan then set over a low heat.
Cook the pickle until the sugar has dissolved, stirring occasionally then increase the heat to medium-high & bring to the boil.
Boil the pickle for 3-4 minutes, until reduced & syrupy then turn the heat back down to low & add in the jalapeños.
Cook the jalapeños, stirring regularly until they have started to soften & darken in colour. This will take around 5 minutes.
Using a slotted spoon, remove the jalapeños from the vinegar & transfer into a clean jar.
Set the pan of vinegar back over a medium-high heat & bring to the boil. Cook for 4-5 minutes, until syrupy then pour over the jalapeños.
Let the candied jalapeños cool completely then refrigerate for a day before using.