While both Pecorino Romano and Parmesan are hard, salty, Italian cheeses, they are not the same. Pecorino Romano is made from sheep's milk and has a stronger, tangier flavor, while Parmesan is made from cow's milk and has a nuttier, milder flavor. For this recipe, we prefer Pecorino Romano for its bold, salty bite, but you can substitute it with Parmesan if you prefer.