Pour the washed beans in a pot with not too much water and let it boil 3-4 min.
Remove from the stove, discard the water and pour in cold water - up to 2 fingers from the top of the pot.
Turn the stove on again and once boiling, lower the heat.
Shortly before the beans are fully cooked, mix together water, the flour and black pepper and pour slowly into the beans while stirring.
Finally, add salt, spearmint and parsley.