Preheat oven to 400°F. Unfold 1 pastry sheet on each of 2 baking sheets. Top with ham, cheese, and mushrooms, leaving 1/2-inch plain border. Whisk eggs, rosemary, pepper, salt, and nutmeg in bowl. Whisk in sour cream. Spoon egg mixture over toppings on each pastry. Bake until pastries are puffed and golden and toppings are set, about 25 minutes.