For the paste: Pound the green onions, chile, mint leaves, allspice berries, thyme leaves, lime juice, olive oil, salt, and pepper in a mortar and pestle, grinding them as hard as you can.
For the lamb: Wash the lamb rumps and pat them dry with paper towels. Mix the spice paste with the lamb in a bowl, using your hands to get it well coated. Cover the bowl, and let the meat rest for at least 1 hour, or overnight, in the refrigerator.
Heat the oil in a medium-sized heavy-bottomed saucepan. Once hot, add the lamb. Immediately cover the pan with a lid, and turn the heat down to medium. Cook for 5 minutes.
Swirl the water in the bowl in which the lamb was marinated and add the liquid to the pan. Cover once again and cook for another 5 minutes. In a small bowl, combine the stout and brown sugar. Now, remove the lid, add the stout mixture, and bring everything to a boil. Immediately reduce the heat to low, and cook for around 8 minutes, or until the lamb is cooked through. The cooking juices should evaporate, leaving you with a lovely, dark and glossy stew with a bitter, hot, and sweet flavor.
Garnish the dish with fresh mint sprigs and serve with Rice and Peas.
To make Rice and Peas: First break into the coconut. Choose one of the 3 eyes that you are most likely to be able to puncture. Cook's Note: Youll see them at one end. Only one will work.
Try to penetrate the eye with a strong, sharp-tipped knife. If the hole doesnt give, try the others. Pour the coconut water out through its eye and set it aside in a small bowl. Smash the coconut open, and, using a small, sharp knife, lever the coconut flesh away from the shell. Cook's Note: Doing this outside against some concrete is a good idea.
Grate the coconut into a bowl. Pour 2 3/4 cups water over the shreds, and stir. Strain the coconut flesh from the water in fistfuls, and squeeze out all its juices over the bowl. Place the squeezed clumps of grated coconut into a sieve, transfer the coconut water to a saucepan and tip the squeezed coconut back into the bowl. Cover the coconut shreds with the remaining clean water and, once again, lift the coconut flesh up from the water in fistfuls and squeeze out all its juices. Transfer the prepared coconut water to the saucepan, and discard the squeezed-out flesh.
If desired, incorporate the fresh coconut water to the saucepan at this stage. Then, add the black beans, onion, chile, green onion, garlic, allspice berries, thyme, butter, and adjust their seasonings with salt, and black pepper. Bring everything to a boil, cover, and then turn down the heat to medium, and simmer for 15 minutes.
Meanwhile, rinse the rice under cold running water until the water runs clear. Drain the rice, and then add the rice to the saucepan with the reserved prepared coconut water or base in the saucepan. You may need to add some additional water to bring the liquid about 1-inch above the level of the rice. Season the cooking liquid with salt, and black pepper, bring it to a boil, and then cover the rice immediately. Turn the heat down to its lowest level, and simmer for 15 to 20 minutes. Don't stir it and don't peek inside!
Once the rice is tender, fish out the chile, green onion, and thyme sprigs, fluff the rice with a fork, and serve immediately.