- Heat 3 tablespoons olive oil in a large pot over medium-high heat. Season lamb and chicken with salt and pepper; cook in batches with onions in the hot oil until browned, about 2 minutes per side. Transfer to a large plate.
- Scrape the bottom of the pot with a wooden spoon to release browned bits. Return lamb and chicken to the pot. Pour in enough water to cover; add turmeric, cumin and ground coriander. Cover and bring to the boil. Reduce heat to medium; simmer for 20 minutes.
- Stir potatoes, turnips and carrots into the pot. Simmer, covered, until vegetables start to soften, about 10 minutes. Mix in tomato puree and ras el hanout; cook for 10 minutes. Stir in chickpeas, courgettes and fresh coriander; continue cooking, covered, until courgette is tender, about 5 minutes.
- Bring 700ml water to the boil in a saucepan; remove from heat and stir in couscous and butter. Cover saucepan and let stand until water is absorbed completely, 5 to 10 minutes. Fluff couscous with a fork and stir in 1 tablespoon olive oil. Transfer to a serving dish.
- Ladle 2 scoops of cooking liquid into a bowl; mix in harissa until smooth.
- Scoop vegetables onto a serving plate. Scoop lamb and chicken onto a separate plate. Serve alongside couscous, harissa sauce and remaining cooking liquid in the pot.
Homemade ras el hanout:
Mix 1 teaspoon ground cumin, 1 teaspoon ground ginger, 1 teaspoon ground turmeric, 3/4 teaspoon ground cinnamon, 3/4 teaspoon freshly ground black pepper, 1/2 teaspoon ground white pepper, 1/2 teaspoon ground coriander, 1/2 teaspoon ground cayenne, 1/2 teaspoon ground nutmeg and 1/4 teaspoon ground cloves.