The night before, rinse red beans in cold water and soak in 3 to 4 cups of cold water overnight. Separately, rinse salted pig tails and soak in about 6 cups of cold water overnight.
The next day, drain water from pig tails, place in pot, and cover with fresh cold water. Bring to a boil for 3 to 5 minutes then drain water.
Add 6 cups fresh cold water to pot and bring to a boil. Lower the heat and cook about 30 minutes. Add red beans (including the water they were soaked in) and beef to pot.
Cover pot and cook meat and beans on a low boil until very tender, about 1 hour (keep the liquid level the same by adding boiling water to pot as liquid evaporates). When the beans are almost tender, add the coconut milk.
In a frying pan on medium heat, melt butter and sauté onion, red and green bell pepper, scotch bonnet pepper, and scallion (white part only, chopped) until onion is transparent, about 3 minutes. Add all the sautéed ingredients to pot on low boil along with remaining scallion, sprigs of thyme, black pepper, and pimento. Remove scotch bonnet pepper after a few minutes, or to taste depending on spice level you want to achieve.
In a separate bowl, make small spindle-shape dumplings (called spinners) by mixing ingredients until combined. Add more flour and water as needed—when you can roll the dough in your hands and it sticks a little bit but doesn't leave pasty residue on your hand, that's when you know it's ready.
Take about a tablespoon of dough and roll in between both palms to make a long, roughly 1/2-inch thick dumpling, and add to the pot. Simmer, stirring often, until stew thickens and dumplings are cooked.
Remove large pieces of scallion, sprigs of thyme, and pimento. Serve hot over steamed white rice.