Melt butter in a 10-inch skillet over medium heat. Add onion; sauté 5 minutes. Stir in saffron; cook 1 minute. Add rice; stir to coat with butter and onions. Add vermouth and 2 cups chicken stock. Simmer, covered, and add the remaining broth 1/2 cup at a time, until rice is tender. The entire cooking time is about 30 minutes. The rice should be bound lightly together with a little of the cooking liquid. Stir in pistachios and Parmesan and serve immediately.