Heat the oil in a pan and sauté the sliced leeks and garlic cloves for 3-4 minutes before stirring in the mushrooms. Cook for another 2 minutes. Stir in the butterbeans, smoked paprika and flour and cook for 2 minutes.
Pour in the stock and stir whilst bringing to the boil. Simmer for 10-12 minutes, until the leeks are soft. Stir in the soured cream or yogurt and serve with brown rice.