Heat the oven to 190°C (Gas Mark 5 / 375°F).
If your sun-dried tomatoes are packed in oil, lay them on a piece of kitchen paper for a few minutes to drain any excess oil.
Roll out the puff pastry, and cut into 4 rectangles. Score a line around each rectangle, about 1cm in from the edge, to form a border (don’t cut all the way through the pastry). Prick the centre of each rectangle a few times with a fork.
Spread each pastry rectangle with a little basil pesto. Roughly chop the sun-dried tomatoes and fresh mozzarella, and scatter over the pastry. Add a little black pepper, then bake for around 15-20 minutes, until the pastry is crispy and the cheese is golden brown.
While the tarts are baking, add the pine nuts to a dry frying pan, and toast over a medium heat for a few minutes, stirring regularly, until golden brown.
Serve the pesto tomato tarts with the toasted pine nuts and some fresh basil, if desired.