Preheat oven to 300 degrees F.
Cut off 2-slices (about 1/4-cup) of pork and set aside for Spanish rice.
Make at least 12-slits in pork with the tip of a very sharp knife. Put 1 clove of garlic in each slit. In a small bowl, mix together the sazon and adobo seasonings. Add 1/4-cup sofrito and stir together. Rub over entire pork shoulder.
Place pork in large roasting pan, wrap with foil and cook for 3 hours. Remove the foil and crank oven up to 400 degrees F and let cook additional 20 minutes until desired crispness.
For the rice:
In large saucepan on high heat, saute onions and reserved pork in the butter until lightly browned. Add sazon, adobo, rice, water and reserved sofrito.
Cook about 10 minutes on high or until the water begins to evaporate to almost the level of the rice. Add pigeon peas and cilantro. Cover with lid, reduce heat to low and let cook until water is totally evaporated and rice is tender. Remove from heat.
Can keep in the refrigerator for up to 10 days. Do not stir at any point.