Preheat the oven to 350 degrees. Cut the short rib into chunks about 2x4 inches and season with salt. Heat an ovenproof deep-sided skillet or dutch oven with the oil over medium hight-heat. Sear the short ribs on all sides and remove them from the skillet. Add onions and garlic to the pan and brown. Add the peppercorns and coriander seed and toast for 1 minute. Stir in the chili powder and paprika. Then add the tomato paste. Cook the tomato paste for 2-5 minutes. Stir almost constantly so as not to burn, turning down the heat if necessary. Add the stock and oregano. Add the short ribs back to the pot and bring to a simmer. Cover and place in the oven for 2 1/2-3 hours, flipping over every hour. Short ribs should be fall-apart tender. Make the sopes, crema, and onions while the beef is cooking.