Place the peas in a large bowl. Remove any stones and discard. Add cold water to cover by several inches. Soak overnight or 8 hours. Or, for a quick soak, wash and sort the peas. Place in a large stockpot and add water to cover, about 3 quarts. Bring to a rolling boil over high heat. Remove from the heat and let soak for 1 hour. Drain soaked or quick-soaked peas, discarding the water.
Meanwhile, heat stock in a pot over high heat. Add flavoring agent, onion, and optional chili pepper. Reduce heat to simmer and cook for 25-30 minutes to flavor the stock. Add the drained peas. Season with salt and pepper. Bring to a boil over high heat, reduce heat to simmer and cook uncovered until just tender – almost al dente - and about 2 cups of liquid remain, 45 minutes to 1 hour. Taste and adjust the seasoning with salt and pepper.
Add the rice to the pot, cover, and simmer over low heat for about 20 minutes. Do not remove the lid during this part of cooking. Remove the pot from the heat and allow the rice to steam, still covered, for another 10 minutes. Remove the cover, fluff with a fork, and taste and adjust for seasoning. Serve immediately with hot sauce on the side.