Soak the split peas overnight in a bowl of water. Place the chopped onion in a mug with butter, cover and microwave for 2 minutes. Then drain the split peas and place with the onion in a rice cooker and cover well with fresh water. Cook for about an hour or until the peas are soft . Add the carrot and press “cook” again. In about 20 minutes everything will be tender. Add salt if desired.