How to Make It
In a large saucepan, heat the oil until shimmering. Add the onions and a generous pinch of salt and cook over moderate heat, stirring occasionally, until lightly browned, about 12 minutes. Add the beef, lamb and garlic and cook, breaking up the meat with a wooden spoon, until the meat is cooked through, 8 to 10 minutes. Stir in the 1 cup of pistachios, the harissa, cumin, paprika, coriander, turmeric, cinnamon, cardamom, ginger, cloves and a generous pinch each of salt and pepper. Cover and simmer over low heat, stirring occasionally, until the meat and pistachios are very tender, about 2 hours.
In a medium bowl, whisk the yogurt with the tahini; season with salt and pepper. Swipe some of the yogurt into shallow bowls. Top with the ragù, garnish with pistachios and serve with roasted tomatoes and pita.