Place beans in a saucepan and cover with a generous quantity of water. Bring to a boil and cook, uncovered, until beans are tender, about 1 hour. Meanwhile, melt butter in a heavy bottomed stockpot, add onions and cook until golden brown, about 5 minutes. Add garlic and cook 2 more minutes. Add dry spices and fry gently until aromas are released.

Drain excess water off beans and add to stockpot, along with salt and stock or water. Cook gently over low heat until flavors are combined, about 20 minutes. Add tomatoes, brown sugar, and oregano, and cook an additional 10 minutes. Serve hot garnished with plain yogurt.