The secret ingredient is butter! I add a little bit to this "pesto rosso" with sun dried tomatoes and basil, to give it an extra rich flavour.
Parmesan cheese is not truly vegetarian, as it contains animal rennet. To make this dish 100% vegetarian, omit the cheese or find a suitable vegetarian substitute made without animal rennet. In supermarkets look for the 'parmesan style hard cheeses' which are suitable for vegetarians.