Spiced Harissa Ragù with Tahini Yogurt

Name: Spiced Harissa Ragù with Tahini Yogurt
Ingredients: 1/4 cup vegetable oil; 3 large onions, finely chopped; Kosher salt; Pepper; 1 pound ground beef; 1 pound ground lamb; 10 garlic cloves, finely chopped; 1 cup shelled pistachios, coarsely chopped, plus more for garnish; 1 tablespoon harissa; 2 1/2 teaspoons ground cumin; 1 1/2 teaspoons hot paprika; 1 teaspoon ground coriander; 1/2 teaspoon ground turmeric; 1/2 teaspoon ground cinnamon; 1/2 teaspoon ground cardamom; 1/4 teaspoon ground ginger; 1/8 teaspoon ground cloves; 1 cup whole-milk yogurt; 1/4 cup tahini; Roasted cherry tomatoes and warm pita, for serving