Put all the ingredients, apart from the butter, in a large non-stick saucepan with a lid. Add 800ml cold water and mix well until the herbs are evenly distributed. Season generously with salt and pepper, dot the butter all over the top, put the lid on, and cook for 25-30 mins over a low-medium heat (use a low heat on a gas cooker) until the rice on top is cooked. Fluff up with a fork and serve. It's a bonus if you get a 'tahdig' (Persian for rice crust), which you can serve in pieces on top of the rice.