Make marinade: Combine ingredients for marinade in a measuring jug. Whisk well.
Add pork: Place pork tenderloin in freezer bag and pour marinade on top. Close bag well, then lightly massage marinade into pork.
Marinate: Marinate in the fridge for at least 1 hour, and up to 3 days.°F.
Cook: Remove pork tenderloin from bag, discarding marinade, rosemary and bag. Cook tenderloin on the grill or in oven until cooked to a minimum temperature of 145°F, followed by a 3 minute rest (see cooking instructions in notes below). Slice to serve.