Preheat oven to 180° Mix the washed, unpeeled halved potatoes, the halved onions and with the garlic that has its outer dry layer of peel removed and that has been cut in half across. Add the rosemary, tarragon,cumin salt and pepper. Add the oil, mix again until everything is coated well. All is placed into a ovenproof deep baking tray or large pie dish.