Preheat the oven to 400˚F. In a small bowl, stir together the jam, mustard, vinegar, rosemary and/or chilli flakes. Season the pork tenderloin(s) with salt, place on a parchment-lined baking sheet and spread with the jam mixture. (There should be enough for 2, if you want to cook 2 tenderloins at once on the same sheet.)
Bake for 25-30 minutes, or until the internal temperature reaches 160˚F. Let rest for 10 minutes, covered with foil, before slicing.