In large nonstick frying pan over medium-high heat, stir pistachios until fragrant and lightly toasted, about 2 minutes. Set aside. Wash spinach in plenty of cold water to remove any grit. Discard tough stems. Shake off excess water. In frying pan, heat stock and add onions. saute until tender, about 3 to 5 minutes. Add spinach and nutmeg. saute until spinach wilts, about 2 minutes. Add pistachios. Toss lightly. Sprinkle with cheese.