Chicken Curry with Cashews

Name: Chicken Curry with Cashews
Ingredients: 1/2 stick (1/4 cup) unsalted butter; 2 medium onions, finely chopped (2 cups); 2 large garlic cloves, finely chopped; 1 tablespoon finely chopped peeled fresh ginger; 3 tablespoons curry powder; 2 teaspoons salt; 1 teaspoon ground cumin; 1/2 teaspoon cayenne; 1 (3 1/2- to 4-pound) chicken, cut into 10 serving pieces; 1 (14.5-ounce) can diced tomatoes; 1/4 cup chopped fresh cilantro; 3/4 cup cashews (1/4 pound); 3/4 cup plain whole-milk yogurt; Accompaniment: cooked basmati or jasmine rice; Garnish: chopped fresh cilantro