Preheat the oven to 200°C / fan oven 180°C / Gas Mark 6. Lightly grease a large baking sheet.
Unroll the puff pastry sheet and cut into six equal rectangles. Using a sharp knife, score a border within each pastry rectangle about 2cm from the edge, being careful to avoid cutting right through the pastry. Place on the baking sheet.
Spread the inner rectangle of each piece of pastry with a little pesto sauce, and then sprinkle the cheese on top. Share the tomatoes between the tarts, then season with salt and pepper to taste.
Brush the pastry edges with beaten egg or milk, then bake for about 15 minutes. Sprinkle the pine nuts over the tarts, and then bake for a further four or five minutes, until the pastry is risen and crisp. Cool for a few minutes, then serve, garnished with shavings of Parmigiano Reggiano.
Cook’s tip: Add a little Parma Ham or pepperoni for a tasty variation.