Pour about 500ml water into a small saucepan, bring to the boil and take off the heat. Add vinegar and sun dried tomatoes, give it a stir, cover and let sit for 10 minutes until tomatoes are soft. (You can omit this step, if you are using sun dried tomatoes in oil).
Meanwhile toast the pine nuts in a dry frying pan over medium heat until lightly browned, shaking the pan from time to time to ensure that the nuts don't burn. Remove from the pan and set aside.
Drain tomatoes and transfer to a food processor. Add olive oil, basil, butter, garlic and pine nuts and process until smooth. Stir in Parmesan and salt to taste.
Transfer to a sterilised jar, then pour a little olive oil on top to seal the pesto from the air and tightly screw on the lid. Use within a week or so.
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.