Cook up the beans normally (soak, boil, simmer). Pour yams into pot, including liquid. Smash lightly. Add tomato puree, stir through. Add spices, stir through. Add cooked beans, stir through. Simmer for for a few minutes to mellow out. (*) Beans: I keep a 'bean bucket' of mixed beans, usually including pea beans, black-eyed peas, pinto beans, split peas, lentils, navy beans, pinto beans; often including great northern beans, roman beans, pink beans, chili beans, barley, and others. Whenever there's room in the bucket I pour in a bag of something that seems underrepresented. This would probably be better with fresh yams and tomatoes, but the canned yams were on sale half price the day after Thanksgiving...