Scoop the tomatillos into a slow cooker and spread them in an even layer. Scatter on the garlic, jalapenos and half of the cilantro. Sprinkle evenly with 1 ½ tsp salt.
In a large bowl, combine the pork and Worcestershire sauce, mixing until the cubes are well coated. Distribute the meat over the tomatillo mixture. Cover and slow cook on high for 6 hours.
With a pair of tongs, remove the pork to a bowl. Tip or ladle the sauce mixture into a blender and add the remaining cilantro. Cover loosely and blend until smooth; return the mixture to the slow cooker. Stir in the drained beans, taste and add salt as necessary; Stir in a little water if the sauce has thickened beyond the consistency of a light cream soup. Add a little sugar if the sauce is too tart. Return the meat to the pot, let everything warm through and serve.
This dish can be cooked in a Dutch oven instead of the slow cooker. In a medium large (4 to 6 quart) heavy pot or Dutch oven, layer the tomatillos, flavorings and meat as described above. Cover with the sauce, set the lid in place and braise in a 3000F oven for 2 ½ to 3 hours, until the pork is completely tender. Complete the dish as described above.
The beans can be replaced with potatoes or small sweet turnips (cut into wedges) or carrots (2 inch lengths cut into sticks). Toss them with a little salt and place them on top of the sauce ingredients before layering in the pork. Take them out with the meat while you finish the sauce.
Add a big handful of spinach to the blender when pureeing the sauce; a few Tbsp of Mexican Crema or heavy cream works magic on this spinach enhanced sauce. Epazote may be used in place of the cilantro.
This dish is perfect made with 2 pounds boneless, skinless chicken thighs. Or replace the pork shoulder with 1 inch pieces of beef chuck; double the cilantro and use 2 poblanos. The beef will benefit greatly from browning before slow cooking.
Either brown the cubed pork in a little oil in a single layer in a large skillet, or spread it out on an oiled baking sheet (with sides) and slide it close up under a broiler. Slide the browned meat into the slow cooker.