Drain and rinse the chickpeas and butterbeans, bring two pans of water to the boil and cook them separately: this should take anywhere between 20 and 40 minutes. Drain and set aside.
Put the butter, onion and garlic in a large pan and place on a medium heat. Cook for 20 minutes, stirring occasionally, until soft and golden brown. Stir in the turmeric, ½ teaspoon of salt and some black pepper and remove a third of this mix from the pan to use later.
Add the chickpeas and butterbeans to the pan, then add the split peas and stock. Simmer for about 35 minutes, skimming the froth occasionally, or until the peas are tender.
Add the herbs, spring onion and spinach, stir well and cook for another 15 minutes; add more stock or water if the soup is very thick. Add the noodles and cook for about 10 minutes so that they are just done. Stir in the soured cream and vinegar and serve at once, garnished with a teaspoon of soured cream per portion and the reserved cooked onion. Serve lime halves to squeeze over every portion.