Preheat oven to 425º. Grease large baking sheet. Working with one sheet of the puff pastry, keeping remaining sheet wrapped and cold, roll out on lightly floured surface to 14-inch square. Brush with thin layer of mustard. Cover with half of the prosciutto slices, slightly overlapping and leaving 1/2-inch border around edges. Sprinkle with one cup of the cheese. Roll pastry tightly, from long side. Pinch seams to seal and tuck ends under. Repeat with remaining pastry sheet. Cut into 1/2-inch pieces and place, cut side up, 1-inch apart on prepared baking sheet. Bake 10 to 15 minutes or until golden brown. Makes 10-12 servings.