Soak the barberries in twice their volume of water for about 10 minutes. Drain and remove the stems. Place a heavy based saucepan on medium heat, add the barberries or cranberries, if using, sugar, verjuice or cider vinegar, if using, and cinnamon. Mix well, bring to a boil then reduce heat and simmer for 5 minutes, till just syrupy but not completely set. Remove from heat, mix in the pistachios and allow to cool. Transfer to a serving plate, cover and set aside.
In a mixing bowl, combine the lamb, chili, garlic, cumin, coriander, cinnamon, pomegranate molasses, coriander, salt and pepper mixing well till all incorporated. Pinch off a very small portion for testing and shape into a patty. Add a small frying pan to medium heat, drizzle a tablespoon of oil and fry the patty about 2-3 minutes on each side. Once cooked, allow to cool a couple of minutes then taste. Adjust seasoning accordingly, cover and set aside in fridge overnight. Bring to room temperature (about 1 hour) before grilling. Shape the meat into 6 individual patties. Pre-heat grill or start BBQ and grill about 2-4 minutes on each side, depending on how much you prefer them cooked. Alternatively, you can cook them in a griddle pan or saute pan over medium-high heat on the stove top for a couple of minutes each side. Serve each burger on a lettuce leave topped with the barberry-pistachio relish.
