Heat a pan to high heat with some oil. Sear the beef cubes and place in slow cooker. Add harissa, cinnamon, turmeric, cumin, paprika, ginger, and pepper and coat the beef. Bring the pan down to medium heat and saute the onion, bell peppers, carrots, and garlic until golden. Add these to the slow cooker along with the potatoes, bay leaf, tomatoes, raisins, and beef stock. Dice the cilantro stems and throw them in too. In a small dish, combine the flour with 1 tbsp beef stock, whisk until combined, and add to the slow cooker. Turn the slow cooker to low and cook until beef is tender, about 7-8 hours, stirring once or twice.

Combine yogurt with 1 tbsp olive oil, 1 tsp dried parsley, and 1 tbsp diced cilantro.

Add some of the stew into a bowl, place a heap of herbed yogurt, and sprinkle with sumac and more chopped cilantro.