1. Preheat oven to 200°C/400°F/Gas 6. Lightly grease two or three flat baking trays.
2. Sieve the flour, salt and pepper into a large bowl. Coarsely rub in the butter. Add sufficient cold water to mix to a soft dough.
3. Turn onto a floured board and gently knead. Roll into an oblong. Fold in a third of the pastry then fold it again over itself so it is a third of the size. Roll into an oblong again and repeat three times.
4. Roll out thinly and cut into about 6 x 13cms/6" rounds. A side plate is ideal for this!
5. Place on prepared tins, prick well with a fork then brush on the beaten egg. Place into the preheated oven for 15 minutes until brown. Place on a wire tray to cool.
6. Thinly slice the tomatoes and mozzarella. Place the tomatoes around the base then the cheese. Add a few basil leaves. Drizzle olive oil on top and sprinkle with salt & pepper.
7. Reduce the oven to 180°C/350°F/Gas 4 and return the tarts to the oven for about 15 minutes until cooked and cheese has melted.
8. Remove from oven, place on a plate and garnish with more basil leaves and basil pesto.